Bonded abrasive article

ABSTRACT

The present invention relates to a bonded abrasive article comprising specific shaped abrasive particles and a bonding medium comprising a vitreous bond. The present invention also relates to the use of an article according to the present invention in grinding applications, in particular in high performance grinding applications and to the use of an article according to the present invention for abrading a workpiece material particularly a workpiece material selected from steels, non-ferrous metals, and alloys. In addition, the present invention relates to a method for abrading a workpiece, the method comprising frictionally contacting at least a portion of an abrasive article according to the invention with a surface of a workpiece; and moving at least one of the workpiece or the abrasive article to abrade at least a portion of the surface of the workpiece.

The present invention relates to bonded abrasive articles, particularlythose which are useful in high performance grinding.

Abrasive machining using bonded abrasive articles (such as grindingwheels) continues to develop its capabilities. This development hascreated an increasing demand for high-performance grinding wheels:wheels which can remove material faster at exacting tight tolerances,but without causing damage at the workpiece, thus able to providereductions in grinding cycle time and lower grinding costs per part.

Bonded abrasive articles have abrasive particles bonded together by abonding medium. The main types of bonding systems used to make bondedabrasive articles are: resinoid, vitrified, and metal. Resinoid bondedabrasives utilize an organic binder system (e.g., phenolic bindersystems) to bond the abrasive particles together to faint the shapedmass. Another major type are bonded abrasive articles (for examplevitrified bonded wheels) in which a vitreous binder system is used tobond the abrasive particles together. These bonds are usually vitrifiedat temperatures between 700° C. to 1500° C. Metal bonded abrasivearticles typically utilize sintered or plated metal to bond the abrasiveparticles. Vitrified bonded abrasive articles are different fromresinoid bonded abrasive articles in that they use a vitreous phase tobond the abrasive grain and thus are processed at substantially highertemperatures. Vitrified bonded abrasive articles can withstand highertemperatures in use and are generally more rigid and brittle thanresinoid bonded wheels.

Bonded abrasives are three-dimensional in structure and typicallyinclude a shaped mass of abrasive particles, held together by thebinder. Such shaped mass can be, for example, in the form of a wheel,such as a grinding wheel. Ideal bonded abrasive articles have a longlife time and are able to abrade the workpiece with constant cut overtime. However, when the abrasive particles are worn and dulled, theseabrasive particles are expelled from the bonded abrasive to expose new,fresh cutting abrasive particles. In the ideal situation, the bondedabrasive article is self-sharpening. However, in reality, particularly,when the forces get high enough, the bonded abrasive articles can breakdown, breaking and ejecting grit particles and the grinding power drawndecreases beyond the starting value of the grinding application as thebonded abrasive article wears away rapidly and looses its preferredshape. Bonded abrasive articles therefore typically show cyclicalgrinding curves (grinding power consumption as a function of grindingtime). At the end point of a grinding cycle dressing of the bondedabrasive article (such as a grinding wheel) has to be set up in order toavoid defects at the workpiece to be abraded and in order to provide forconstant abrading performance of the bonded abrasive article. Dressingis typically performed using a dressing tool such as a diamond dressingtool. Frequent dressing cycles are undesirable since the productionprocess has to be interrupted frequently which will add on costs,besides reducing service life of the wheel. What is desired in theindustry is a bonded abrasive article requiring a minimum of dressingcycles resulting in a long total service life of the wheel. Such anarticle typically draws a minimum of power when operating.

Vitrified bonded grinding wheels incorporating irregularly shaped (forexample, crushed) abrasive particles are known to be useful for abradingworkpieces such as hardened and unhardened metal components. However,the dressing cycles of these abrasives articles can be more frequentthan desired, i.e., resharpening has to be set up more frequently toavoid dulling of the grains. Sometimes constant grinding performance interms of workpiece quality and/or long dressing cycles cannot beprovided, particularly under severe grinding conditions, e.g., high feedrates. In particular, in case of a grinding cycle not having a phase ofsubstantially constant grinding performance (for example in terms ofmaterial removal rate) over a period of time it can be difficult toachieve constant grinding results of the workpiece to be abraded.

What is desired in the industry is a bonded abrasive article, forexample, a grinding wheel, that has an improved service life and canprovide constant grinding results (particularly in terms of surfacequality of the workpiece) over a long period of time, particularly undersevere grinding conditions.

Surprisingly, it has been found that shaped abrasive particles incombination with a vitrified bond can provide abrasive articles whichcan solve the aforementioned problems. In particular, such articles havebeen found to be particularly effective in high performance grindingapplications.

The present invention relates to a bonded abrasive article comprisingshaped abrasive particles and a bonding medium comprising a vitreousbond, said shaped abrasive particles each comprising a first side and asecond side separated by a thickness t, wherein said first sidecomprises a first face having a perimeter of a first geometric shape.The thickness t is preferably equal to or smaller than the length of theshortest side-related dimension of the particle.

Typically, the ratio of the length of the shortest side relateddimension to the thickness of said particle is at least 1:1.

The present invention also relates to the use of the bonded abrasivearticles in high performance grinding applications and to a method forabrading a workpiece.

FIG. 1 illustrates a graph of the grinding power consumption as afunction of the grinding time for Type III Wheels of Example I (Examples1A-1, 1A-2, 2A-1 and 3A-1 and Comparative Examples Ref. 1A-2, Ref. 2A-1,Ref. 3A-1, and Ref. 3A-2) using the conditions of Test Series (I).

FIG. 2 illustrates a graph of the grinding power consumption as afunction of the grinding time for the Type VII Wheels of Example I(Examples 1B-1, 1B-2, 2B-1 and 3B-1) using the conditions of Test Series(I).

FIG. 3 illustrates a graph of the grinding power consumption as afunction of the grinding time for Type III Wheels of Example 1 (Examples1A-1, 1A-2, 2A-1 and 3A-1 and Comparative Examples Ref. 1A-2, Ref. 2A-1,Ref. 3A-1, and Ref. 3A-2) using the conditions of Test Series (II).

FIG. 4 illustrates a graph of the grinding power consumption as afunction of the grinding time for Type VII Wheels of Example I (Examples1B-1, 1B-2, 2B-1 and 3B-1) using the conditions of Test Series (II).

FIG. 5 shows a graph illustrating the surface roughness Ra obtained forType III Wheels of Example I (Examples 1A-1, 1A-2, 2A-1, 3A-1, andComparative Examples Ref. 1A-2, Ref. 2A-1, Ref. 3A-1, and Ref. 3A-2).

FIG. 6A is a schematic top view of exemplary shaped abrasive particle320.

FIG. 6B is a schematic side view of exemplary shaped abrasive particle320.

FIG. 6C is a cross-sectional top view of plane 3-3 in FIG. 6B.

FIG. 6D is an enlarged view of side edge 327 a in FIG. 6C.

While the above-identified drawing figures set forth several embodimentsof the present disclosure, other embodiments are also contemplated, asnoted in the discussion. The figures may not be drawn to scale. Likereference numbers may have been used throughout the figures to denotelike parts.

As used herein, forms of the words “comprise”, “have”, and “include” arelegally equivalent and open-ended. Therefore, additional non-recitedelements, functions, steps or limitations may be present in addition tothe recited elements, functions, steps, or limitations.

As used herein, the term “abrasive dispersion” means a precursor (intypical cases an alpha alumina precursor) that can be converted into anabrasive material (for example, alpha alumina) that is introduced into amold cavity. The composition is referred to as an abrasive dispersionuntil sufficient volatile components are removed to bring aboutsolidification of the abrasive dispersion.

As used herein, the term “precursor shaped abrasive particle” means theunsintered particle produced by removing a sufficient amount of thevolatile component from the abrasive dispersion, when it is in the moldcavity, to form a solidified body that can be removed from the moldcavity and substantially retain its molded shape in subsequentprocessing operations.

As used herein, the term “shaped abrasive particle”, means an abrasiveparticle with at least a portion of the abrasive particle having apredetermined shape that is replicated from a mold cavity used to formthe shaped precursor abrasive particle. Except in the case of abrasiveshards (e.g. as described in US Patent Application Publication Nos.2009/0169816 and 2009/0165394), the shaped abrasive particle willgenerally have a predetermined geometric shape that substantiallyreplicates the mold cavity that was used to form the shaped abrasiveparticle. Shaped abrasive particle as used herein excludes abrasiveparticles obtained by a mechanical crushing operation.

As used herein, the term “nominal” means: of, being, or relating to adesignated or theoretical size and/or shape that may vary from theactual.

With respect to the three-dimensional shape of the abrasive particles inaccordance with the present invention, the length shall mean the longestparticle dimension, the width shall mean the maximum particle dimensionperpendicular to the length. The thickness as referred to herein is alsotypically perpendicular to length and width.

As used herein, the term “thickness”, when applied to a particle havinga thickness that varies over its planar configuration, shall mean themaximum thickness. If the particle is of substantially uniformthickness, the values of minimum, maximum, mean, and median thicknessshall be substantially equal. For example, in the case of a triangle, ifthe thickness is equivalent to “a”, the length of the shortest side ofthe triangle is preferably at least “2a”. In the case of a particle inwhich two or more of the shortest facial dimensions are of equal length,the foregoing relationship continues to hold. In most cases, the shapedabrasive particles are polygons having at least three sides, the lengthof each side being greater than the thickness of the particle. In thespecial situation of a circle, ellipse, or a polygon having very shortsides, the diameter of the circle, minimum diameter of the ellipse, orthe diameter of the circle that can be circumscribed about the veryshort-sided polygon is considered to be the shortest facial dimension ofthe particle.

For further illustration, in case of a tetrahedral-shaped abrasiveparticle, the length would typically correspond to the side length ofone triangle side, the width would be the dimension between the tip ofone triangle side and perpendicular to the opposite side edge and thethickness would correspond to what is normally referred to as “height ofa tetrahedron”, that is, the dimension between the vertex andperpendicular to the base (or first side).

If an abrasive particle is prepared in a mold cavity having a pyramidal,conical, frusto-pyramidal, frusta-conical, truncated spherical, or atruncated spheroidal shape, the thickness is determined as follows: (1)in the case of a pyramid or cone, the thickness is the length of a lineperpendicular to the base of the particle and running to the apex of thepyramid or cone; (2) in the case of a frusto-pyramid or frusto-cone, thethickness is the length of a line perpendicular to the center of thelarger base of the frusto-pyramid or of the frusto-cone and running tothe smaller base of the frusto-pyramid or of the frusto-cone; (3) in thecase of a truncated sphere or truncated spheroid, the thickness is thelength of a line perpendicular to the center of the base of thetruncated sphere or truncated spheroid and running to the curvedboundary of the truncated sphere or truncated spheroid.

The length of the shortest side-related dimension of the particle is thelength of the shortest facial dimension of the base of the particle (ifthe particle has only one base, typically the first face) or the lengthof the shortest facial dimension of the larger base of the particle (ifthe particle has two bases, for example in cases where the second sidecomprises a second face).

As used herein in referring to shaped abrasive particles, the term“length” refers to the maximum dimension of a shaped abrasive particle.In some cases the maximum dimension may be along a longitudinal axis ofthe particle, although this is not a necessary requirement. “Width”refers to the maximum dimension of the shaped abrasive particle that isperpendicular to the length. “Thickness” refers to the dimension of theshaped abrasive particle that is perpendicular to the length and width.

As used herein the term “circular sector” or “circle sector” refers tothe portion of a disk enclosed by two radii and an arc, including minorsectors and major sectors.

As used herein the term “circular segment” refers to an area of a circleinformally defined as an area which is “cut off” from the rest of thecircle by a secant or a chord. The circle segment constitutes the partbetween the secant and an arc, excluding the circle's center. This iscommonly known as Meglio's Area.

As used herein the term “drop shape” is intended to refer to a shapehaving a perimeter (the path that surrounds the drop shape area) thatcan be described as consisting of one vertex and one curved line,wherein the vertex is formed at the point wherein the ends of the curvedline meet.

As used herein the term “rhombus” refers to a quadrilateral having fouredges of equal length and wherein opposing vertices have included anglesof equal degrees as seen in FIGS. 1 and 3 of WO 2011/068714.

As used herein the term “rhomboid” refers to a parallelogram wherein thetwo intersecting edges on one side of the longitudinal axis are ofunequal lengths and a vertex between these edges has an oblique includedangle as seen in FIG. 4 of WO 2011/068714.

As used herein the term “kite”, as seen in FIG. 5 of WO 2011/068714,refers to a quadrilateral wherein the two opposing edges above atransverse axis are of equal length and the two opposing edges below thetransverse axis are of equal length, but have a different length thanthe edges above the transverse axis. If one took a rhombus and moved oneof the opposing major vertices either closer to or further away from thetransverse axis a kite is formed.

As used herein the term “superellipse” refers to a geometric figuredefined in the Cartesian coordinate system as the set of all points (x,y) defined by Lame's curve having the formula

${{\frac{x}{a}}^{n} + {\frac{y}{b}}^{n}} = 1$

where n, a and b are positive numbers. When n is between 0 and 1, thesuperellipse looks like a four-armed star with concave edges (withoutthe scallops) as shown in FIG. 2 of WO 2011/068714. When n equals 1, arhombus a=b or a kite a< >b is formed. When n is between 1 and 2 theedges become convex.

As used herein the term “secondary abrasive particles” is intended togenerally refer to abrasive particles which differ from the shapedabrasive particles to be used in accordance with the present invention

The term “hard materials” as used in the present invention is intendedto refer to materials which can typically be characterized as having aKnoop Hardness of 3500 kg_(f)/mm² or less (typically, about 1500 toabout 3000 kg_(f) μmnf).

The term “superhard materials” as used in the present invention isintended to refer to materials which can be typically characterized ashaving a Knoop Hardness of more than 3500 kg_(f)/mm² (typically, about4000 to about 9000 kg_(f)/mm²).

The term “superabrasives” as used in the present invention is intendedto refer to abrasive materials which can be typically characterized ashaving a Knoop Hardness of 4500 or more than 4500 kg_(f)/mm²) (typically4700 to about 9000 kg_(f)/mm²).

Most oxide ceramics have a Knoop hardness in the range of 1000 to 1500kg_(f)/mm² (10-15 GPa), and many carbides are over 2000 kg_(f)/mm² (20GPa). The method for determining Knoop Hardness is specified in ASTMC849, C1326 & E384.

The present invention relates to a bonded abrasive article comprisingspecific shaped abrasive particles (which can be typically characterizedas thin bodies) and a bonding medium comprising a vitreous bond. Thepresent invention also relates to the use of an article according to thepresent invention in grinding applications, in particular in highperformance grinding applications and to the use of an article accordingto the present invention for abrading a workpiece material particularlya workpiece material selected from steels, non-ferrous metals, andalloys. In addition, the present invention relates to a method forabrading a workpiece, the method comprising frictionally contacting atleast a portion of an abrasive article according to the invention with asurface of a workpiece; and moving at least one of the workpiece or theabrasive article (while in contact) to abrade at least a portion of thesurface of the workpiece.

In accordance with the present invention, the bonded abrasive articlecomprises shaped abrasive particles. Three basic technologies that havebeen employed to produce abrasive grains having a specified shape are(1) fusion, (2) sintering, and (3) chemical ceramic.

Any one of these basic technologies or any combination of two or all ofthese technologies may be used in order to provide shaped abrasiveparticles for use in the present invention.

The materials that can be made into shaped abrasive particles of theinvention include any suitable hard or superhard material known to besuitable for use as an abrasive particle.

Accordingly, in one embodiment, the shaped abrasive particles comprise ahard abrasive material. In another embodiment, the shaped abrasiveparticles comprise a superhard abrasive material. In yet otherembodiments, the shaped abrasive particles comprise a combination ofhard and superhard materials.

Specific examples of suitable abrasive materials include known ceramicmaterials, carbides, nitrides and other hard and superhard materialssuch as aluminum oxide (for example alpha alumina) materials (includingfused, heat treated, ceramic and sintered aluminum oxide materials),silicon carbide, titanium diboride, titanium nitride, boron carbide,tungsten carbide, titanium carbide, diamond, cubic boron nitride (CBN),garnet, alumina-zirconia, sol-gel derived abrasive particles, ceriumoxide, zirconium oxide, titanium oxide or a combination thereof.

The most useful of the above are typically based on aluminum oxide, and:in the specific descriptions that follow the invention may beillustrated with specific reference to aluminum oxide. It is to beunderstood, however, that the invention is not limited to aluminum oxidebut is capable of being adapted for use with a plurality of differenthard and superhard materials.

With respect to the three basic technologies for preparing shapedabrasive particles (i.e., fusion, sintering and chemical ceramictechnologies), in the present invention, the shaped abrasive particlesmay be based on one or more material(s) prepared by any one of thesetechnologies, i.e. on one or more fused, sintered or ceramic materials,with a preferred material being aluminum oxide (preferably alphaaluminum oxide). In other words, preferred shaped abrasive particlesaccording to the invention are based on alumina, i.e. such particleseither consist of alumina or are comprised of a major portion thereof,such as for example greater than 50%, for example 55 to 100%, or 60 to80%, more preferably 85 to 100% by weight of the total weight of theabrasive particle. The remaining portion may comprise any material whichwill not detract from the shaped abrasive particle acting as anabrasive, including but not limited to hard and superhard materials asoutlined in the foregoing. In some preferred embodiments, the shapedabrasive particles consist of 100% aluminum oxide. In yet otherpreferred embodiments, the shaped abrasive particles comprise at least60% by weight aluminum oxide or at least 70% by weight of aluminumoxide. Useful shaped abrasive particles may, for example, include butare not limited to particles which comprise a major portion (for example50% or more and preferably 55% or more by weight) of fused aluminumoxide and a minor portion (for example, less than 50% and preferablyless than 45% by weight) of an abrasive material different from fusedaluminum oxide (for example zirconium oxide).

It is also within the scope of the present invention to use abrasiveparticles that have a surface coating for example of inorganic particlesthereon. Surface coatings on the shaped abrasive particles may be usedto improve the adhesion between the shaped abrasive particles and abinder material in abrasive articles, or can be used to aid inelectrostatic deposition of the shaped abrasive particles. In oneembodiment, surface coatings as described in U.S. Pat. No. 5,352,254(Celikkaya) in an amount of 0.1 to 2 percent surface coating to shapedabrasive particle weight may be used. Such surface coatings aredescribed in U.S. Pat. No. 5,213,591 (Celikkaya et al.); U.S. Pat. No.5,011,508 (Wald et al.); U.S. Pat. No. 1,910,444 (Nicholson); U.S. Pat.No. 3,041,156 (Rowse et al.); U.S. Pat. No. 5,009,675 (Kunz et al.);U.S. Pat. No. 5,085,671 (Martin et al.); U.S. Pat. No. 4,997,461(Markhoff-Matheny et al.); and U.S. Pat. No. 5,042,991 (Kunz et al.).Additionally, the surface coating may prevent the shaped abrasiveparticle from capping. Capping is the term to describe the phenomenonwhere metal particles from the workpiece being abraded become welded tothe tops of the shaped abrasive particles. Surface coatings to performthe above functions are known to those skilled in the art.

In the present invention, it is preferred to use shaped abrasiveparticles produced by chemical ceramic technology, i.e., ceramic shapedabrasive particles. However, the present invention is not limited to theuse of such particles.

In one embodiment, the ceramic shaped abrasive particles comprise alphaalumina, i.e. the particles are alpha alumina based ceramic shapedparticles.

In one embodiment, the ceramic shaped abrasive particles comprisesol-gel derived alumina based abrasive particles. Both seeded andnon-seeded sol-gel derived alumina based abrasive particles can besuitably used in accordance with the present invention. However, in someinstances, it may be preferred to use non-seeded sol-gel derived aluminabased abrasive particles.

The shaped abrasive particles of the present invention each have asubstantially precisely formed three-dimensional shape. Typically, theshaped abrasive particles generally have a predetermined geometricshape, for example one that substantially replicates the mold cavitythat was used to form the shaped abrasive particle.

Typically, the shaped abrasive particles can be characterized as thinbodies. As used herein the term thin bodies is used in order todistinguish from elongated or filamentary particles (such as rods),wherein one particle dimension (length, longest particle dimension) issubstantially greater than each of the other two particle dimensions(width and thickness) as opposed to particle shapes useful in thepresent invention wherein the three particle dimensions (length, widthand thickness as defined herein) are either of the same order ofmagnitude or two particle dimensions (length and width) aresubstantially greater than the remaining particle dimension (thickness).Conventional filamentary abrasive particles can be characterized by anaspect ratio, that is the ratio of the length (longest particledimension) to the greatest cross-sectional dimension (the greatestcross-sectional dimension perpendicular to the length) of from about 1:1to about 50:1, preferably of from about 2:1 to about 50:1 and moretypically greater than about 5:1 to about 25:1. Furthermore, suchconventional filamentary abrasive particles are characterized by across-sectional shape (the shape of a cross section taken perpendicularto the length or longest dimension of the particle) which does not varyalong the length.

In contrast hereto, shaped abrasive particles according to the presentinvention can be typically characterized by a cross-sectional shape thatvaries along the length of the particle. Variations can be based on sizeof the cross-sectional shape or on the form of the cross-sectionalshape.

The abrasive particles generally each comprise a first side and a secondside separated by a thickness t. The first side generally comprises (andmore typically is) a first face (in typical cases a planar face) havinga perimeter of a first geometric shape.

Preferably, the thickness t is equal to or smaller than the length ofthe shortest side-related dimension of the particle (the shortestdimension of the first side and the second side of the particle; thelength of the shortest side-related dimension of the particle may alsobe referred to herein as the length of the shortest facial dimension ofthe particle).

In typical cases, the second side comprises a vertex separated from thefirst side by thickness t, or the second side comprises a ridge lineseparated from the first side by thickness t, or the second sidecomprises a second face separated from the first side by thickness t.For example, the second side may comprise a vertex and at least onesidewall connecting the vertex and the perimeter of the first face(illustrative examples include pyramidal shaped particles, for exampletetrahedral-shaped particles). Alternatively, the second side maycomprise a ridge line and at least one sidewall connecting the ridgeline and the perimeter of the first face (illustrative examples includeroof-shaped particles). Alternatively, the second side may comprise asecond face and at least one sidewall (which may be a sloping sidewall)connecting the second face and the first face (illustrative examplesinclude triangular prisms or truncated pyramids).

Blends of different shaped abrasive particles in accordance with thepresent invention can be used in the bonded abrasive articles of thepresent invention. A blend of shaped abrasive particles can comprise afirst plurality of shaped abrasive particles in accordance with thepresent invention and a second plurality of shaped abrasive particles inaccordance with the present invention wherein the particles of the firstplurality are different from the second plurality. Differences can forexample be selected based on the shape or grade or chemical compositionof the abrasive particle.

The thickness t may be the same (for example in embodiments wherein thefirst and second sides comprise parallel planar faces) or vary over theplanar configuration of the particle (for example in embodiments whereinone or both of the first and second sides comprise non-planar faces orin embodiments wherein the second side comprises a vertex or a ridgeline as discussed in more detail later herein).

In most cases, the ratio of the length of the shortest side-relateddimension of the shaped abrasive particle to the thickness of the shapedabrasive particle is at least 1:1 but can range from 1:1 to 10:1, morepreferably from 2:1 to 8:1 and most preferably from 3:1 to 6:1. Thisratio is also referred to herein as primary aspect ratio.

The dimension of the thickness of the particles is not particularlylimited. For example in typical cases, the thickness can be about 5micrometers or more, or about 10 micrometers or more, or about 25micrometers or more, or about 30 micrometers or more, or even about 200micrometers or more. The upper limit of the thickness can be selected tobe about 4 mm or less, or about 3 mm or less for large particles, orabout 1600 micrometers or less, or about 1200 micrometers or less, orabout 100 micrometers or less, or about 500 micrometers or less or about300 micrometers or less or even about 200 micrometers or less.

The shaped abrasive particles are typically selected to have a length ina range of from 0.001 mm to 26 mm, more typically 0.1 mm to 10 mm, andmore typically 0.5 mm to 5 mm, although other lengths may also be used.In some embodiments, the length may be expressed as a fraction of thethickness of the bonded abrasive article in which it is contained. Forexample, the shaped abrasive particle may have a length greater thanhalf the thickness of the bonded abrasive wheel. In some embodiments,the length may be greater than the thickness of the bonded abrasivewheel.

The shaped abrasive particles are typically selected to have a width ina range of from 0.001 mm to 26 mm, more typically 0.1 mm to 10 mm, andmore typically 0.5 mm to 5 mm, although other dimensions may also beused.

The shaped abrasive particles can have various volumetric aspect ratios.The volumetric aspect ratio is defined as the ratio of the maximum crosssectional area passing through the centroid of a volume divided by theminimum cross sectional area passing through the centroid.

For some shapes, the maximum or minimum cross sectional area may be aplane tipped, angled, or tilted with respect to the external geometry ofthe shape. For example, a sphere would have a volumetric aspect ratio of1.000 while a cube will have a volumetric aspect ratio of 1.414. Ashaped abrasive particle in the form of an equilateral triangle havingeach side equal to length A and a uniform thickness equal to A will havea volumetric aspect ratio of 1.54, and if the uniform thickness isreduced to 0.25 A, the volumetric aspect ratio is increased to 2.64. Itis believed that shaped abrasive particles having a larger volumetricaspect ratio have enhanced cutting performance.

In various embodiments of the invention, the volumetric aspect ratio forthe shaped abrasive particles can be greater than about 1.15, or greaterthan about 1.50, or greater than about 2.0, or between about 1.15 toabout 10.0, or between about 1.20 to about 5.0, or between about 1.30 toabout 3.0.

The abrasive particles are preferably in the shape of thinthree-dimensional bodies having various three-dimensional shapes.Typical examples include particles (typically, thin bodies) in the formof flat triangles, flat rectangles, flat triangles which have at leastone face and more preferably two faces that is/are shaped inwardly (forexample recessed or concave), as discussed in more detail later herein.

The first side generally comprises (and more typically is) a first facehaving a perimeter of a first geometric shape.

For example, the first geometric shape can be selected from geometricshapes having at least one vertex, more typically two or more,preferably three or more, most preferably three or four vertices.

Suitable examples for geometric shapes having at least one vertexinclude polygons (including equilateral, equiangular, star-shaped,regular and irregular polygons), lense-shapes, lune-shapes, circularshapes, semicircular shapes, oval shapes, circular sectors, circularsegments, drop-shapes and hypocycloids (for example super ellipticalshapes). Specific examples for suitable polygonal geometric shapesinclude triangular shapes and quadrilateral shapes (for example asquare, a rectangle, a rhombus, a rhomboid, a trapezoid, a kite, or asuperellipse).

The vertices of suitable quadrilateral shapes can be further classifiedas a pair of opposing major vertices that are intersected by alongitudinal axis and a pair of opposing minor vertices located onopposite sides of the longitudinal axis. Shaped abrasive particleshaving a first side having this type of quadrilateral shape can becharacterized by an aspect ratio of a maximum length along alongitudinal axis divided by the maximum width transverse to thelongitudinal axis of 1.3 or greater, preferably 1.7 to about 5. Thisaspect ratio is also referred to herein as secondary aspect ratio.

In some embodiments it is particularly preferred that the firstgeometric shape is selected from triangular shapes, such as an isoscelestriangular shape or, more preferably, an equilateral triangular shape.

In other embodiments, the first geometric shape is selected fromquadrilateral shapes, preferably from the group of a square, arectangle, a rhombus, a rhomboid, a trapezoid, a kite, or asuperellipse, more preferably from the group of a rectangle, a rhombus,a rhomboid, a kite or a superellipse.

For the purposes of this invention geometric shapes are also intended toinclude regular or irregular polygons or stars wherein one or more edges(parts of the perimeter of the face) can be arcuate (either of towardsthe inside or towards the outside, with the first alternative beingpreferred). Hence, for the purposes of this invention, triangular shapesalso include three-sided polygons wherein one or more of the edges(parts of the perimeter of the face) can be arcuate, i.e., thedefinition of triangular extends to spherical triangles and thedefinition of quadrilaterals extends to superellipses.

The second side may comprise (and preferably is) a second face. Thesecond face may have a perimeter of a second geometric shape.

The second geometric shape may be the same or be different to the firstgeometric shape. Preferably the second geometric shape is selected tohave substantially the same shape as the first geometric shape and ispreferably arranged in a congruent way with the first geometric shape(although the size or area of the geometric shapes may be different,i.e. the one face may be larger than the other one).

In other words, as used herein the terms “substantially the same shape”or “substantially identical shapes” are intended to include the casewherein the area encompassed by said shapes may be different in size.

As used herein with respect to the preferred case of substantiallyidentical first and second geometric shapes, the term “arranged in acongruent way with the first geometric shape” is intended to include thecase wherein the first and the second geometric shapes are slightlyrotated against each other, although it is preferred that saidsubstantially identical first and second geometric shapes are perfectlyaligned or only slightly rotated against each other. The degree (orangle of rotation) depends on the particular geometric shape of thefirst face and of the second face and the thickness of the particle.Acceptable angles of rotation may range from 0 to +/−30 degrees,preferably from 0 to +/−15, more preferably from 0 to +/−10 degrees.Most preferably, the angle of rotation is about 0 degrees (for example0+/−5 degrees).

Examples of suitable geometric shapes of the perimeter of the secondface include shapes as exemplified in the foregoing with respect to thefirst geometric shapes.

It is particularly preferred that the first and preferably also thesecond geometric shape is selected from triangular shapes, such as anisosceles triangular shape or, more preferably, an equilateraltriangular shape.

The first face may be substantially planar or the second face (ifpresent) may be substantially planar. Also, both faces may besubstantially planar. In many typical cases, the first face is planar(and identical to the first side).

Alternatively, at least one of the first and the second face (ifpresent) may be a non-planar face. Also both faces may be non-planarfaces.

For example, one or both of the first and the second face (if present)could be shaped inwardly (for example recessed or concave) or could beshaped outwardly (for example convex).

For example, the first face (or the second face, if present) can beshaped inwardly (for example be recessed or concave) and the second face(if present, or the first face) can be substantially planar.Alternatively, the first face (or the second face, if present) can beshaped outwardly (for example be convex) and the second face (ifpresent, or the first face) can be shaped inwardly (for example berecessed or concave), or, the first face can be shaped inwardly (forexample be recessed or concave) and the second face (if present) canalso be shaped inwardly (for example be recessed or concave).

The first face and the second face (if present) can be substantiallyparallel to each other. Alternatively, the first face and the secondface (if present) can be nonparallel, for example such that imaginarylines tangent to each face would intersect at a point (as in theexemplary case wherein one face is sloped with respect to the otherface).

The second face is typically connected to the perimeter of the firstface by at least one sidewall which may be a sloping sidewall, as willbe discussed later in more detail. The sidewall may comprise one or morefacets, which are typically selected from quadrilateral facets.

Specific examples of shaped particles having a second face includeprisms (for example triangular prisms) and truncated pyramids.

In some embodiments, the second side comprises a second face and fourfacets that form a sidewall (draft angle alpha between the sidewall andthe second face equals 90 degrees) or a sloping sidewall (draft anglealpha between the sidewall and the second face greater than 90 degrees).As the thickness, t, of the shaped abrasive particle having a slopingsidewall becomes greater, the shaped abrasive particle resembles atruncated pyramid when the draft angle alpha is greater than 90 degrees.

The shaped abrasive particles can comprise at least one sidewall, whichmay be a sloping sidewall. Typically, the first face and the second faceare connected to each other by the at least one sidewall.

In other embodiments the ridge line and the first face are connected toeach other by the at least one sidewall.

In even other embodiments, the vertex and the first face are connectedto each other by the at least one sidewall.

In some embodiments, more than one (for example two or three) slopingsidewall can be present and the slope or angle for each sloping sidewallmay be the same or different. In some embodiments, the first face andthe second face are connected to each other by a sidewall. In otherembodiments, the sidewall can be minimized for particles where the facestaper to a thin edge or point where they meet instead of having asidewall.

The sidewall can vary and it generally forms the perimeter of the firstface and the second face (if present). In case of a sloping sidewall, itforms a perimeter of the first face and a perimeter of the second face(if present). In one embodiment, the perimeter of the first face and thesecond face is selected to be a geometric shape (preferably a triangularshape), and the first face and the second face are selected to have thesame geometric shape, although, they may differ in size with one facebeing larger than the other face.

A draft angle alpha between the second face and the sloping sidewall ofthe shaped abrasive particle can be varied to change the relative sizesof each face. In various embodiments of the invention, the area or sizeof the first face and the area or size of the second face aresubstantially equal. In other embodiments of the invention, the firstface or second face can be smaller than the other face.

In one embodiment of the invention, draft angle alpha can beapproximately 90 degrees such that the area of both faces aresubstantially equal. In another embodiment of the invention, draft anglealpha can be greater than 90 degrees such that the area of the firstface is greater than the area of the second face. In another embodimentof the invention, draft angle alpha can be less than 90 degrees suchthat the area of the first face is less than the area of the secondface. In various embodiments of the invention, the draft angle alpha canbe between approximately 95 degrees to approximately 130 degrees, orbetween about 95 degrees to about 125 degrees, or between about 95degrees to about 120 degrees, or between about 95 degrees to about 115degrees, or between about 95 degrees to about 110 degrees, or betweenabout 95 degrees to about 105 degrees, or between about 95 degrees toabout 100 degrees.

The first face and the second face can also be connected to each otherby at least a first sloping sidewall having a first draft angle and by asecond sloping sidewall having a second draft angle, which is selectedto be a different value from the first draft angle. In addition, thefirst and second faces may also be connected by a third sloping sidewallhaving a third draft angle, which is a different value from either ofthe other two draft angles. In one embodiment, the first, second andthird draft angles are all different values from each other. Forexample, the first draft angle could be 120 degrees, the second draftangle could be 110 degrees, and the third draft angle could be 100degrees.

Similar to the case of an abrasive particle having one sloping sidewall,the first, second, and third sloping sidewalls of the shaped abrasiveparticle with a sloping sidewall can vary and they generally form theperimeter of the first face and the second face.

In general, the first, second, and third, draft angles between thesecond face and the respective sloping sidewall of the shaped abrasiveparticle can be varied with at least two of the draft angles beingdifferent values, and desirably all three being different values. Invarious embodiments of the invention, the first draft angle, the seconddraft angle, and the third draft angle can be between about 95 degreesto about 130 degrees, or between about 95 degrees to about 125 degrees,or between about 95 degrees to about 120 degrees, or between about 95degrees to about 115 degrees, or between about 95 degrees to about 110degrees, or between about 95 degrees to about 105 degrees, or betweenabout 95 degrees to about 100 degrees.

The sloping sidewall can also be defined by a radius, R, instead of thedraft angle alpha (as illustrated in FIG. 5B of US Patent ApplicationNo. 2010/0151196). The radius, R, can be varied for each of thesidewalls.

Additionally, the various sloping sidewalls of the shaped abrasiveparticles can have the same draft angle or different draft angles.Furthermore, a draft angle of 90 degrees can be used on one or moresidewalls. However, if a shaped abrasive particle with a slopingsidewall is desired, at least one of the sidewalls is a sloping sidewallhaving a draft angle of about greater than 90 degrees, preferably 95degrees or greater.

The sidewall can be precisely shaped and can be for example eitherconcave or convex. Alternatively, the sidewall (top surface) can beuniformly planar. By uniformly planar it is meant that the sidewall doesnot have areas that are convex from one face to the other face, or areasthat are concave from one face to the other face. For example, at least50%, or at least 75%, or at least 85% or more of the sidewall surfacecan be planar. The uniformly planar sidewall provides better defined(sharper) edges where the sidewall intersects with the first face andthe second face, and this is also thought to enhance grindingperformance.

The sidewall may also comprise one or more facets, which are typicallyselected from triangular and quadrilateral facets or a combination oftriangular and quadrilateral facets.

The angle beta between the first side and the sidewall can be between 20degrees to about 50 degrees, or between about 10 degrees to about 60degrees, or between about 5 degrees to about 65 degrees.

The second side may comprise a ridge line. The ridge line is typicallyconnected to the perimeter of the first face by at least one sidewallwhich may be a sloping sidewall, as discussed in the foregoing. Thesidewall may comprise one or more facets, which are typically selectedfrom triangular and quadrilateral facets or a combination of triangularand quadrilateral facets.

The ridge line may be substantially parallel to the first side.Alternatively, the ridge line may be non-parallel to the first side, forexample such that an imaginary line tangent to the ridge line wouldintersect the first side at a point (as in the exemplary case whereinthe ridge line is sloped with respect to the first face).

The ridge line may be straight lined or may be non-straight lined, as inthe exemplary case wherein the ridge line comprises arcuate structures.

The facets may be planar or non-planar. For example at least one of thefacets may be non-planar, such as concave or convex. In someembodiments, all of the facets can be non-planar facets, for exampleconcave facets.

Specific examples of shaped particles having a ridge line includeroof-shaped particles, for example particles as illustrated, in FIG. 4Ato 4C of WO 2011/068714). Preferred roof-shaped particles includeparticles having the shape of a hip roof, or hipped roof (a type of roofwherein any sidewalls facets present slope downwards from the ridge lineto the first side. A hipped roof typically does not comprise verticalsidewall(s) or facet(s)).

In some embodiments, the first geometric shape is selected from aquadrilateral having four edges and four vertices (for example from thegroup consisting of a rhombus, a rhomboid, a kite, or a superellipse)and the second side comprises a ridge line and four facets forming astructure similar to a hip roof. Thus, two opposing facets will have atriangular shape and two opposing facets will have a trapezoidal shape.

The second side may comprise a vertex and at least one sidewallconnecting the vertex and the perimeter of the first face. The at leastone sidewall may be a sloping sidewall, as discussed in the foregoing.The sidewall may comprise one or more facets, which are typicallyselected from triangular facets. The facets may be planar or non-planar.For example at least one of the facets may non-planar, such as concaveor convex. In some embodiments, all of the facets can be non-planarfacets, for example concave facets.

Illustrative examples include pyramidal-shaped particles, for exampletetrahedral-shaped particles or particles as illustrated in FIG. 1A to1C and FIG. 2A to 2C of WO 2011/068714. The thickness, t, of the shapedabrasive particles can be controlled to select an angle, beta, betweenthe first side and the sidewall (or facets). In various embodiments ofthe invention, the angle beta between the first side and the sidewall(or facets) can be between 20 degrees to about 50 degrees, or betweenabout 10 degrees to about 60 degrees, or between about 5 degrees toabout 65 degrees.

In typical embodiments the second side comprises a vertex and a sidewallcomprising and more typically consisting of triangular facets forming apyramid. The number of facets comprised by the sidewall will depend onthe number of edges present in the first geometric shape (defining theperimeter of the first face). For example, pyramidal shaped abrasiveparticles having a first side characterized by a trilateral firstgeometric shape will generally have three triangular facets meeting inthe vertex thereby forming a pyramid, and pyramidal shaped abrasiveparticles having a first side characterized by a quadrilateral firstgeometric shape will generally have four triangular facets meeting inthe vertex thereby forming a pyramid, and so on.

In some embodiments, the second side comprises a vertex and four facetsforming a pyramid. In exemplary embodiments, the first side of theshaped abrasive particle comprises a quadrilateral first face havingfour edges and four vertices with the quadrilateral preferably beingselected from the group consisting of a rhombus, a rhomboid, a kite, ora superellipse. The shape of the perimeter of the first face (i.e., thefirst geometric shape) can be preferably selected from the above groupssince these shapes will result in a shaped abrasive particle withopposing major vertices along the longitudinal axis and in a shape thattapers from the transverse axis toward each opposing major vertex.

The degree of taper can be controlled by selecting a specific aspectratio for the particle as defined by the maximum length, L, along thelongitudinal axis divided by the maximum width, W, along the transverseaxis that is perpendicular to the longitudinal axis. This aspect ratio(also referred to herein as “secondary aspect ratio”) should be greaterthan 1.0 for the shaped abrasive particle to taper as may be desirablein some applications. In various embodiments of the invention, thesecondary aspect ratio is between about 1.3 to about 10, or betweenabout 1.5 to about 8, or between about 1.7 to about 5. As the secondaryaspect ratio becomes too large, the shaped abrasive particle can becometoo fragile.

In some embodiments, it is possible to slightly truncate one or more ofthe vertices as shown by dashed lines 42 in FIG. 1 of WO 2011/068714 andmold the shaped abrasive particles into such a configuration. In theseembodiments, if the edges where the truncation occurs can be extended toform one or more an imaginary vertices that then completes the claimedquadrilateral, the first side is considered to be the claimed shape. Forexample, if both of the major opposing vertices were truncated, theresulting shape would still be considered to be a rhombus because whenthe edges are extended past the truncation they form two imaginaryvertices thereby completing the rhombus shape for the first side.

Another exemplary class of shaped abrasive particles having a secondside comprising a vertex are tetrahedral shaped particles. A tetrahedralshape generally comprises four major sides joined by six common edges,wherein one of the four major sides contacts three other of the fourmajor sides, and wherein the six common edges have substantially thesame length. According to the definitions used herein a tetrahedralshape can be characterized by a first side comprising a equilateraltriangle as a first face and a second side comprising a vertex and asidewall comprising three equilateral triangles as facets connecting thefirst face and the vertex, thereby forming a tetrahedron.

At least one of the four major sides (i.e. the group consisting of thefirst side and the three facets) can be substantially planar. At leastone of the four major sides can be concave, or all the four major sidescan be concave. At least one of the four major sides can be convex orall the four major sides can be convex.

The shaped particles of this embodiment typically have tetrahedralsymmetry. The shaped abrasive particles of this embodiment arepreferably substantially shaped as regular tetrahedrons.

It is preferred that the shaped abrasive particles comprise at least oneshape feature selected from: an opening (preferably one extending orpassing through the first and second side); at least one recessed (orconcave) face or facet; at least one face or facet which is shapedoutwardly (or convex); at least one side comprising a plurality ofgrooves; at least one fractured surface; a low roundness factor (asdescribed later herein); a perimeter of the first face comprising one ormore corner points having a sharp tip; a second side comprising a secondface having a perimeter comprising one or more corner points having asharp tip; or a combination of one or more of said shape features.

In preferred embodiments the shaped abrasive particles comprise at leastone of the aforementioned shape features in combination with asubstantially triangular shape of the perimeter of the first andoptionally the second face.

In other preferred embodiments the shaped abrasive particles comprise atleast one of the aforementioned shape features in combination with asubstantially quadrilateral first geometric shape.

In other preferred embodiments, the shaped abrasive particle comprises acombination of two or more (for example, of three, four, five or more)of the recited shape features. For example, the abrasive particle cancomprise an opening and a first face that is shaped outwardly (orconvex) and a recessed (or concave) second face; a second facecomprising a plurality of grooves and a low roundness factor; or anopening and a first face that is shaped outwardly (or convex) and arecessed (or concave) second face.

The shaped abrasive particles preferably have a perimeter of the firstand optionally of the second face that comprises one or more cornerpoints having a sharp tip. Preferably, all of the corner pointscomprised by the perimeter(s) have sharp tips. The shaped abrasiveparticles preferably also have sharp tips along any edges that may bepresent in a sidewall (for example between two meeting facets comprisedby a sidewall).

The sharpness of a corner point can be characterized by the radius ofcurvature along said corner point, wherein the radius extends to theinterior side of the perimeter (as illustrated for the exemplary shapedabrasive particle shown in FIG. 6D).

In various embodiments of the invention, the radius of curvature (alsoreferred to herein as average tip radius) can be less than 75 microns,or less than 50 microns, or less than 25 microns. It is believed that asharper edge promotes more aggressive cutting and improved fracturing ofthe shaped abrasive particles during use.

A smaller radius of curvature means that the particle more perfectlyreplicates the edge or corner features of the mold used to prepare theparticle (i.e. of the ideal shape of the particle), i.e. the shapedabrasive particles are much more precisely made. Typically, shapedabrasive articles (in particular, ceramic shaped abrasive particles)made by using a mold of the desired shape provide more precisely madeparticles than methods based on other methods for preparing shapedabrasive particles, such as methods based on pressing, punching orextruding.

FIGS. 6C-6D show the radius of curvature 329 a for sidewall edge 327 a.In general, the smaller the radius of curvature, the sharper thesidewall edge will be.

The shaped abrasive particles may comprise an opening. The opening canpass completely through the first side and the second side.Alternatively, the opening can comprise a blind hole which may not passcompletely through both sides.

In one embodiment, the size of the opening can be quite large relativeto the area defined by the perimeter of the first face or the secondface (if present).

The opening can comprise a geometric shape which may be the same or adifferent geometric shape than that of the first geometric shape and thesecond geometric shape.

An opening ratio of the opening area divided by the face area of thelarger of either the first face or the second face can be between about0.05 to about 0.95, or between about 0.1 to about 0.9, or between about0.1 to about 0.7, between about 0.05 to about 0.5, or between about 0.05to about 0.3. For the purposes of this calculation, the face area isbased on the area enclosed by the perimeter without subtracting any areadue to the opening.

Shaped abrasive particles with an opening can have several benefits oversolid, shaped abrasive particles without an opening. First, the shapedabrasive particles with an opening have an enhanced cut rate as comparedto solid, shaped abrasive particles. Shaped abrasive particles having alarger opening relative to the face size may have enhanced grindingperformance.

The inner surface of the opening can have varying contours. For example,the contour of the inner surface may be planar, convex, or concavedepending on the shape of the upstanding mold element used for themanufacture of the shaped abrasive particle with an opening.Additionally, the inner surface can be tapered such that the size of theopening in each face is different. It is preferred that the innersurface is a tapered surface such that the opening is narrower at thetop of the mold cavity and wider at the bottom of the mold cavity forbest release of the shaped abrasive particles from the mold and toprevent cracking of the shaped abrasive particles during drying.

The opening can be selected to have substantially the same shape as thefirst perimeter. The opening can also be selected to have substantiallythe same shape as the perimeter of the first face and of the perimeterof the second face. Thus, the shaped abrasive particles with an openingcan comprise an integral connection of a plurality of bars joined attheir respective ends to form a closed polygon as illustrated forexample in FIG. 1A or FIG. 5A of US patent Application Publication2010/0151201. Alternatively, the shape of the opening can be selected tobe different than the shape of the first and optionally of the secondperimeter, as illustrated for example in FIG. 5B of US patentApplication Publication 2010/0151201. The size and/or shape of theopening can be varied to perform different functions more effectively.In one embodiment, the shape of the opening comprises a substantiallytriangular shape, more preferably the shape of an equilateral triangle.

Another feature of the shaped abrasive particles with an opening can bean extremely low bulk density as tested by ANSI B74.4-1992 Procedure forBulk Density of Abrasive Grains. Since the opening can significantlyreduce the mass of the shaped abrasive particles without reducing theiroverall size, the resulting bulk density can be extremely low. Moreover,the bulk density of the shaped abrasive particles can be readily changedand controlled by simply varying the size and shape of the opening inthe particles. In various embodiments of the invention, the bulk densityof the shaped abrasive particles with an opening can be less than 1.35g/cm³, or less than 1.20 g/cm³, or less than 1.00 g/cm³, or less than0.90 g/cm³. The shaped abrasive particles may comprise at least onenon-planar face. For example, the first face may be a non-planar face orboth of the first face and the second face may be a non-planar face, orone or both of the first face and the second face could be shapedinwardly (for example recessed or concave) or shaped outwardly (forexample convex).

For example, the first face can be shaped inwardly (for example berecessed or concave) and the second face can be substantially planar.Alternatively, the first face can be shaped outwardly (for example beconvex) and the second face can be shaped inwardly (for example berecessed or concave), or, the first face can be shaped inwardly (forexample be recessed or concave) and the second face can also be shapedinwardly (for example be recessed or concave).

A face which is shaped inwardly (for example a recessed face) maycomprise a substantially planar center portion and a plurality of raisedcorners or upturned points. To further characterize such a face, thecurvature of the first face of the shaped abrasive particles can bemeasured by fitting a sphere using a suitable image analysis programsuch as a non-linear regression curve-fitting program “NLREG”, availablefrom Phillip Sherrod, Brentwood, Tenn., obtained from www.NLREG.com. Arecessed face may comprise a radius of a sphere curve fitted to therecessed face by image analysis. The radius can be between about 1 mm toabout 25 mm, more preferably about 1 mm to about 14 mm or between about2 mm to about 7 mm, when the center of the sphere is vertically alignedabove the midpoint of the first face 24. In one embodiment, the radiusof the fitted sphere to the dish-shaped abrasive particles measured 2.0mm, in another embodiment 3.2 mm, in another embodiment 5.3 mm, and inanother embodiment 13.7 mm.

In one embodiment, the abrasive particles may be described asdish-shaped abrasive particles. In general, the dish-shaped abrasiveparticles comprise typically thin bodies having a first face, and asecond face separated by a sidewall having a varying thickness t. Ingeneral, the sidewall thickness is greater at the points or corners ofthe dish-shaped abrasive particles and thinner at the midpoints of theedges. As such, Tm is less than Tc. In some embodiments, the sidewall isa sloping sidewall having a draft angle alpha greater than 90 degrees asdiscussed in more detail in the foregoing. More than one slopingsidewall can be present and the slope or draft angle for each slopingsidewall may be the same or different for each side of the dish-shapedabrasive particle, as discussed in the foregoing.

In some embodiments, the first face is shaped inwardly (for examplerecessed) and the second face and sidewall are substantially planar. Byrecessed it is meant that that the thickness of the interior of thefirst face, Ti, is thinner than the thickness of the shaped abrasiveparticle at portions along the perimeter.

As mentioned, in some embodiments, the recessed face can have asubstantially flat center portion and a plurality of upturned points ora plurality of raised corners. The perimeter of the dish-shaped abrasiveparticle can be flat or straight at portions between the upturned pointsor corners and the thickness Tc can be much greater than Tm.

In other embodiments, the recessed first face is substantially concavewith three upturned points or corners and a substantially planar secondface (the shaped abrasive particle is plano-concave). The differencebetween Tc and Tm is less and there can be a more gradual transitionfrom the interior of the first face to each upturned point as comparedto the embodiment wherein the first face is recessed and the second faceand sidewall are substantially planar. A recessed face may be the resultfrom the use of a manufacturing method involving sol-gel in a moldcavity and forming a meniscus leaving the first face recessed. Asmentioned, the first face can be recessed such that the thickness, Tc,at the points or corners tends to be greater than the thickness, Ti, ofthe interior of the first face. As such, the points or corners areelevated higher than the interior of the first face.

In various embodiments of the invention, a thickness ratio of Tc/Ti canbe between 1.25 to 5.00, or between 1.30 to 4.00, or between 1.30 to3.00. The thickness ratio can be calculated as described in [0036] of USPatent Application Publication No. 2010/0151195. Triangular dish-shapedabrasive particles have been measured to have thickness ratios between1.55 to 2.32 in some embodiments. Triangular shaped particles producedby the prior art method disclosed in U.S. Pat. No. 5,366,523 (Rowenhorstet al.) have been measured to have thickness ratios between 0.94 to 1.15meaning they are essentially flat and are just as likely to be slightlythicker in the middle as they are to be slightly thinner in the middle.Dish-shaped abrasive particles having a thickness ratio greater than1.20 are statistically different from the Rowenhorst particles at the95% confidence interval.

One or more draft angle(s) alpha between the second face and thesidewall of the dish-shaped abrasive particle can be varied to changethe relative sizes of each face as described in the foregoing.

A preferred embodiment of a dish-shaped abrasive particle is one with arecessed face. The draft angle alpha is approximately 98 degrees and thedish-shaped abrasive particle's perimeter comprises an equilateral,triangle. The sides of each triangle measured approximately 1.4 mm longat the perimeter of the first face.

In one embodiment the thickness t can be more uniform. As such, Tm canbe approximately equal to Tc.

In one embodiment, the first face is convex and the second face isconcave (concavo-convex), for example such that the dish-shaped abrasiveparticle substantially comprises a triangular section of a sphericalshell.

It is believed that the convex face is formed by the sol-gel in the moldcavity releasing from the bottom surface of the mold due to the presenceof a mold release agent such as peanut oil during evaporative drying ofthe sol-gel. The rheology of the sol-gel then results in theconvex/concave formation of the first and second face while theperimeter is formed into shape (preferably, a triangular shape) duringevaporative drying.

In various embodiments of the invention, the radius of a sphere fittedto the concave second face can be between about 1 mm to about 25 mm, orbetween about 1 mm to about 14 mm, or between about 2 mm to about 7 mm,when the center of the sphere is vertically aligned above the midpointof the second face.

In other embodiments of the invention, the first face and the secondface of the dish-shaped abrasive particles can both be recessed. In someembodiments, the dish shaped abrasive particles can be biconcave havinga concave first face and a concave second face. Alternatively, otherrecessed structural geometries can be formed on the second face. Forexample, a plurality of upturned points or a plurality of raised cornerson the second face. In such embodiments, the degree of curvature orflatness of the first face can be controlled to some extent by how thedish-shaped abrasive particles are dried thereby resulting in a recessedor curved first face or a substantially planar first face.

The shaped abrasive particles can comprise a plurality of grooves on oneor both of the first side and the second side. Preferably, the secondside (i.e., one or more sidewalls, faces or facets comprised by thesecond side, and more preferably the second face) comprises a pluralityof grooves.

The shaped abrasive particles can comprise a plurality of ridges on oneor both of the first side and the second side. Preferably, the secondside (i.e., one or more sidewalls, faces or facets comprised by thesecond side, and more preferably the second face) comprises a pluralityof ridges.

The plurality of grooves (or ridges) can be formed by a plurality ofridges (or grooves) in the bottom surface of a mold cavity that havebeen found to make it easier to remove the precursor shaped abrasiveparticles from the mold.

The plurality of grooves (or ridges) is not particularly limited andcan, for example, comprise parallel lines which may or may not extendcompletely across the side. In terms of this aspect ratio, the shapedabrasive particles for use in the invention can be characterized ashaving a ratio of the length of the greatest cross-sectional dimension,of from about 2:1 to about 50:1 and more typically greater than about5:1 to about 25:1. In one embodiment, the plurality of grooves (orridges) comprises parallel lines extending completely across the secondside (preferably across the second face). Preferably, the parallel linesintersect with the perimeter along a first edge at a 90 degree angle.The cross sectional geometry of a groove or ridge can be a truncatedtriangle, triangle, or other geometry as further discussed in thefollowing. In various embodiments of the invention, the depth, D, of theplurality of grooves can be between about 1 micrometer to about 400micrometers. Furthermore, a percentage ratio of the groove depth, D, tothe dish-shaped abrasive particle's thickness, Tc, (D/Tc expressed as apercent) can be between about 0.1% to about 30%, or between about 0.1%to 20%, or between about 0.1% to 10%, or between about 0.5% to about 5%.

In various embodiments of the invention, the spacing between each groove(or ridge) can be between about 1% to about 50%, or between about 1% to40%, or between about 1% to 30%, or between about 1% to 20%, or betweenabout 5% to 20% of a face dimension such as the length of one of theedges of the dish-shaped abrasive particle.

According to another embodiment the plurality of grooves comprises across hatch pattern of intersecting parallel lines which may or may notextend completely across the face. A first set of parallel linesintersects one edge of the perimeter at a 90 degree angle (having apercent spacing of for example 6.25%) of the edge length of thetriangle, and a second set of parallel lines intersects a second edge ofthe perimeter at a 90 degree angle (having a percent spacing of forexample 6.25%) creating the cross hatch pattern and forming a pluralityof raised diamonds in the second face. In various embodiments, the crosshatch pattern can use intersecting parallel or non-parallel lines,various percent spacing between the lines, arcuate intersecting lines,or various cross-sectional geometries of the grooves.

In other embodiments of the invention the number of ridges (or grooves)in the bottom surface of each mold cavity can be between 1 and about100, or between 2 to about 50, or between about 4 to about 25 and thusform a corresponding number of grooves (or ridges) in the shapedabrasive particles.

The shaped abrasive particles may have a low Average Roundness Factor.Such shaped abrasive particles comprise a longitudinal axis extendingfrom a base to the grinding tip of the abrasive article (for example, asshown in FIG. 1 of US Patent Application Publication No. 2010/0319269).The Average Roundness Factor for the shaped abrasive particles can bebetween about 15% to 0%, or between about 13% to 0%, or between about12% to 0%, or between about 12% to about 5%.

The geometric shape of the cross-sectional plane resulting from thetransverse cut (i.e., the cut transversely at 90 degrees to thelongitudinal axis, also simply referred to as cross-sectional shape) ofthe shaped abrasive particles is not particularly limited and can alsovary. A non-circular cross-sectional shape is most preferably used. Acircular cross-sectional shape is round, which is believed to be duller.It is believed that a non-circular cross-sectional shape has improvedgrinding performance since one or more sharp corners can be present andone or more sides could be generally linear similar to a chisel blade.Desirably, the cross-sectional shape is a polygonal shape, including butnot limited to, a triangle, a rectangle, a trapezoid, or a pentagon.

In preferred embodiments (such as in the case of particles having asecond face wherein at least one or preferably both of the first andsecond faces is/are shaped inwardly), the size of the cross-sectionalshape diminishes from the perimeter of the second face towards thecenter of the second face. In this connection, the term “center” is notrestricted to the exact geometric centre of the geometric shape ofsecond face (i.e. the second geometric shape), although this option isalso contemplated and may be preferred in some instances, but isintended to encompass an area generally located in the inside of thegeometric shape of the second face as opposed to the boundaries of thesecond face as defined by the second geometric shape.

In one embodiment, the perimeter of the first and of the second side ofthe (and preferably of the first and of the second face) of the shapedabrasive particle is triangular and the cross-sectional shape istrapezoidal.

The shaped abrasive particles can also comprise at least one fracturedsurface (shaped abrasive particles having at least one fractured surfaceare also referred to herein as fractured shaped abrasive particle orabrasive shard). In other words, the abrasive particles can be shapedabrasive particles, as described in the foregoing, but wherein at leastone surface is a fractured surface.

As compared to the same shaped abrasive particle without at least onefractured surface, the fractured abrasive particle can be considered tocomprise the major part of the original shape of the comparisonparticle, such as for example, at least 60%, or 70% or 80% or 90% byvolume of the original shape. The term original shape means the sameshape but without at least one fractured surface. Typically, theoriginal shape will correspond to the shape of a mold cavity used toprepare the comparative ideally shaped abrasive particle.

Apart from the at least one fractured surface the fractured shapedabrasive particles comprise only precisely formed surfaces defining themajor part of the original shape, and thus exclude particles obtained bya mechanical crushing operation.

In one embodiment, the fractured shaped abrasive particle does notcomprise more than three, preferably more than two fractured surfaces.In another embodiment, the fractured shaped abrasive particle comprisesone fractured surface.

The original shape is not particularly limited and can be selected fromgeometric shapes as defined in the foregoing with respect to abrasiveparticles which do not comprise at least one fractured surface.

Fractured shaped abrasive particles can be formed in a mold having theoriginal shape, such as a triangular cavity. Typically, the mold has aplurality of cavities to economically produce the abrasive shards.

In one example, the shaped abrasive particles can comprise a firstprecisely formed surface, a second precisely formed surface intersectingwith the first precisely formed surface at a predetermined angle alpha,a third surface opposite the first precisely formed surface, and afractured surface.

The first precisely formed surface can be formed by contact with abottom surface of a cavity in a mold (corresponding to the originalshape). The first precisely formed surface substantially replicates thesurface finish and shape of the bottom surface of the cavity. The secondprecisely formed surface of the abrasive shard can be formed by contactwith a sidewall of the cavity in the mold. The sidewall is designed tointersect the bottom surface at a predetermined angle alpha (alsoreferred to as draft angle alpha in the present invention). The secondprecisely formed surface substantially replicates the surface finish andshape of the sidewall of the cavity. The second precisely formed surfaceis molded by contact with the sidewall of the cavity. As such, at leasttwo surfaces of the resulting abrasive shard are precisely formed andthe angle of intersection alpha between the two surfaces is apredetermined angle based on the selected mold geometry. The thirdsurface of the abrasive shard opposite the first precisely formedsurface can be randomly wavy or undulating in appearance since it is incontact with the air after the cavity is filled with an abrasivedispersion. The third surface is not precisely formed since it is notmolded by contact with the cavity. Often, the third surface is createdby scraping or doctoring a top surface of the mold to remove excessiveabrasive dispersion from the mold. The doctoring or scraping stepresults in a subtle waviness or irregularity of the third surface thatis visible under magnification. As such, the third surface is similar toa surface created by extrusion, which is also not precisely formed. Inthe extrusion process, the sol-gel is forced out of a die. As such, thesurfaces of the sol-gel exhibits scrape marks, gouges, and/or scorelines as a result of the extrusion process. Such marks are created bythe relative motion between the sol-gel and the die. Additionally,extruded surfaces from a die can be generally a smooth plane. Incontrast, the precisely formed surfaces can replicate a sinusoidal orother more complex geometrical surface having significant variations inheight along the length of the surface.

The fractured surface of the abrasive shard generally propagates betweenthe first precisely formed surface and the opposing third surface andbetween opposing sidewalls of the cavity when the cavity depth isrelatively small compared to the area of the bottom surface. Thefractured surface is characterized by sharp, jagged points typical of abrittle fracture. The fractured surface can be created by a dryingprocess that cracks or fractures at least the majority of the shapedabrasive particle precursors into at least two pieces while residing inthe cavity. This produces abrasive shards having a smaller size than themold cavity from which they were made. The abrasive shards, once formed,could be reassembled like jigsaw puzzle pieces to reproduce the originalcavity shape of the mold from which they were made. The cracking orfracturing of the precursor abrasive particles is believed to occur byensuring that the surface tension of the abrasive dispersion to thewalls of the cavity is greater than the internal attractive forces ofthe abrasive dispersion as the abrasive dispersion is dried in thecavity.

Another embodiment is a shaped abrasive particle respectively bounded bya polygonal first face (or base), a polygonal second face (or top), anda plurality of sidewalls connecting the base and the top, whereinadjacent sidewalls meet at respective sidewall edges having an averageradius of curvature of less than 50 micrometers. For example, referringto FIGS. 6A-6B, exemplary shaped abrasive particle 320 is bounded by atrigonal base 321, a trigonal top 323, and plurality of sidewalls 325 a,325 b, 325 c connecting base 321 and top 323. Base 321 has sidewalledges 327 a, 327 b, 327 c, having an average radius of curvature of lessthan 50 micrometers. FIGS. 6C-6D show radius of curvature 329 a forsidewall edge 327 a. In general, the smaller the radius of curvature,the sharper the sidewall edge will be. Typically, the base and the topof the shaped abrasive particles are substantially parallel, resultingin prismatic or truncated pyramidal (as shown in FIGS. 6A-6B) shapes,although this is not a requirement. As shown, sides 325 a, 325 b, 325 chave equal dimensions and form dihedral angles with base 321 of about 82degrees. However, it will be recognized that other dihedral angles(including 90 degrees) may also be used. For example, the dihedral anglebetween the base and each of the sidewalls may independently range from45 to 90 degrees, typically 70 to 90 degrees, more typically 75 to 85degrees.

According to particularly preferred embodiments, the shaped abrasiveparticles have a three-dimensional shape of flat triangular platelets orflat rectangular platelets, with flat triangular platelets beingpreferred. Such shaped abrasive particles may also be simply referred toas flat triangles or flat rectangles.

Hence, in particularly preferred embodiments, the shaped abrasiveparticles each comprise a first side and a second side separated by athickness t, wherein said thickness t is preferably equal to or smallerthan the length of the shortest side-related dimension of the particle,wherein said first side comprises (or preferably is) a first face havinga perimeter of a first geometric shape, wherein said second sidecomprises (or preferably is) a second face having a perimeter of asecond geometric shape, and wherein said second side is separated fromsaid first side by thickness t and at least one sidewall connecting saidsecond face and said first face, wherein said first geometric shape andsaid second geometric shapes have substantially identical geometricshapes which may or may not be different in size, wherein said identicalgeometric shapes are both selected either from triangular shapes or fromquadrilateral shapes.

Said first geometric shape is preferably congruent to said secondgeometric shape, as described previously.

It is also preferred that the first and second face of such particlesare substantially planar and substantially parallel to each other.

Preferred triangular and quadrilateral or rectangular shapes are asdefined in the foregoing.

The sidewall can also be as defined in the foregoing. For example, thesidewall can be a non-sloping sidewall (i.e., the size of the firstgeometric shape is identical to the size of the second geometric, shape;for example triangular or rectangular prisms) or a sloping sidewall(i.e., the size of the first geometric shape is not identical to andtypically larger than the size of the second geometric shape; as, forexample, in the case of particles having the shape of truncatedtriangular or rectangular pyramids, as described herein).

According to another particularly preferred embodiment, the shapedabrasive particles are flat triangular platelets (also simply referredto as flat triangles) or flat rectangular platelets (also simplyreferred to as flat rectangles), as described above, but wherein atleast one of the first and the second face is shaped inwardly (forexample recessed or concave).

For example, the first face can be shaped inwardly (for example berecessed or concave) and the second face can be substantially planar orshaped outwardly (for example be convex), or the second face can beshaped inwardly (for example be recessed or concave) and the first facecan be substantially planar or shaped outwardly (for example be convex).

Alternatively and more preferably, the first face can be shaped inwardly(for example be recessed or concave) and the second face can also beshaped inwardly (for example be recessed or concave).

For particles according to this embodiment, the thickness typicallyvaries over the planar configuration of the particle and diminishestowards the “center of the particle”.

Particles according to this embodiment are also typically characterizedby a diminishing area of the cross-sectional shape (perpendicular to thelength) towards the center of the particle.

The term “center of the particle” as used in this connection is to beunderstood in a general way and does not necessarily have to be thegeometric center of the particle, although there might be cases wherethe minimum thickness or the minimum area of the cross-sectional shapecan be found at the geometric center of the particle, as describedpreviously.

The shaped abrasive particles used in the present invention can have anabrasives industry specified nominal grade or a nominal screened grade.

Abrasive particles are generally graded to a given particle sizedistribution before use. Such distributions typically have a range ofparticle sizes, from coarse particles to fine particles. In the abrasiveart this range is sometimes referred to as a “coarse”, “control”, and“fine” fractions. Abrasive particles graded according to abrasiveindustry accepted grading standards specify the particle sizedistribution for each nominal grade within numerical limits. Suchindustry accepted grading standards (i.e., abrasive industry specifiednominal grade) include those known as the American National StandardsInstitute, Inc. (ANSI) standards, Federation of European Producers ofAbrasive Products (FEPA) standards, and Japanese Industrial Standard(JIS) standards.

ANSI grade designations (i.e., specified nominal grades) include: ANSI4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 36, ANSI 46, ANSI 54, ANSI 60,ANSI 70, ANSI 80, ANSI 90, ANSI 100, ANSI 120, ANSI 150, ANSI 180, ANSI220, ANSI 240, ANSI 280, ANSI 320, ANSI 360, ANSI 400, and ANSI 600.FEPA grade designations include F4, F5, F6, F7, F8, F10, F12, F14, F16,F20, F22, F24, F30, F36, F40, F46, F54, F60, F70, F80, F90, F100, F120,F150, F180, F220, F230, F240, F280, F320, F360, F400, F500, F600, F800,F1000, F1200, F1500, and F2000. JIS grade designations include JIS8,JIS12, JIS16, JIS24, JIS36, JIS46, JIS54, JIS60, JIS80, JIS100, JIS150,JIS180, JIS220, JIS240, JIS280, JIS320, JIS360, JIS400, JIS600, JIS800,JIS1000, JIS1500, JIS2500, JIS4000, JIS6000, JIS8000, and JIS10,000.

Alternatively, the shaped abrasive particles can be graded to a nominalscreened grade using U.S.A. Standard Test Sieves conforming to ASTM E-11“Standard Specification for Wire Cloth and Sieves for Testing Purposes.”ASTM E-11 proscribes the requirements for the design and construction oftesting sieves using a medium of woven wire cloth mounted in a frame forthe classification of materials according to a designated particle size.A typical designation may be represented as −18+20 meaning that theshaped abrasive particles pass through a test sieve meeting ASTM E-11specifications for the number 18 sieve and are retained on a test sievemeeting ASTM E-11 specifications for the number 20 sieve. In oneembodiment, the shaped abrasive particles have a particle size such thatmost of the particles pass through an 18 mesh test sieve and can beretained on a 20, 25, 30, 35, 40, 45, or 50 mesh test sieve. In variousembodiments of the invention, the shaped abrasive particles can have anominal screened grade comprising: −18+20, −20+25, −25+30, −30+35,−35+40, −40+45, −45+50, −50+60, −60+70, −70+80, −80+100, −100+120,−120+140, −140+170, −170+200, −200+230, −230+270, −270+325, −325+400,−400+450, −450+500, or −500+635.

The shaped abrasive particles in accordance with the present inventionmay be comprised in a fraction of abrasive particles (or abrasivefraction), also referred to as blend of abrasive particles in thepresent invention (for ease of reference the term “blend” as used hereinis also intended to include the case that the fraction of abrasiveparticles comprises 100% by weight of shaped abrasive particles, basedon the total amount of abrasive particles present in the fraction (orblend).

A blend can comprise one or more types of shaped abrasive particles inaccordance with the present invention and optionally one or more typesof abrasive particles which are generally referred to herein as“secondary abrasive particles” (abrasive particles which differ from theshaped abrasive particles to be used in accordance with the presentinvention). For example, abrasive particles having a shape not inaccordance with the present invention (for example filamentary abrasiveparticles or elongated rods) or conventional non-shaped abrasiveparticles could be used as secondary abrasive particles.

A blend can comprise shaped abrasive particles in accordance with thepresent invention and secondary abrasive particles in any amount.Accordingly, the shaped abrasive particles and the secondary abrasiveparticles may be comprised in a blend, wherein the content of thesecondary abrasive particles may be up to 95% by weight based on thetotal amount of abrasive particles present in the blend or even higher.Thus, in other highly preferred embodiments, the article does notcontain secondary abrasive particles.

In some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent by weight of theblend are shaped abrasive particles according to the present invention,based on the total weight of the blend of abrasive particles.

The secondary abrasive particles may have any suitable particle form (aslong as it is different from the shape of the abrasive particle for usein the invention). Exemplary particle forms include but are not limitedto particle forms obtained by mechanical crushing operation,agglomerated forms and any other forms that differ from the specificabrasive particle shapes as defined herein.

The materials constituting the secondary abrasive particles are notparticularly limited and include any suitable hard or superhard materialknown to be suitable for use as an abrasive particle. Accordingly, inone embodiment, the secondary abrasive particles comprise a majorportion of a hard abrasive material. For example, at least 30%, or atleast 50%, or 60% to 100%, or 90% or more, or 100% by weight of thetotal weight of the secondary abrasive particles are comprised of a hardmaterial. In another embodiment, the secondary abrasive particlescomprise a major portion of a superhard abrasive material. For example,at least 30%, or at least 50%, or 60% to 100%, or 90% or more, or 100%by weight of the total weight of the secondary abrasive particles arecomprised of a superhard material.

Examples of suitable abrasive materials of secondary abrasive particlesinclude but are not limited to known ceramic materials, carbides,nitrides and other hard and superhard materials and include materials,as exemplified herein with respect to shaped abrasive particles, and theshaped abrasive particles of the invention and the secondary abrasiveparticles can be independently selected from particles of suchexemplified materials or any combination thereof.

Representative examples of materials of secondary abrasive particlesinclude for example particles of fused aluminum oxide, e.g., white fusedalumina, heat treated aluminum oxide, ceramic aluminum oxide materialssuch as those commercially available under the trade designation 3MCERAMIC ABRASIVE GRAIN from 3M Company of St. Paul, Minn., sinteredaluminum oxide, silicon carbide (including black silicon carbide andgreen silicon carbide), titanium diboride, boron carbide, tungstencarbide, titanium carbide, diamond, cubic boron nitride, garnet, fusedalumina-zirconia, sol-gel derived abrasive particles (includingsol-gel-derived aluminum oxide particles), cerium oxide, zirconiumoxide, titanium oxide. Examples of sol-gel derived abrasive particlescan be found in U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat.No. 4,623,364 (Cottringer et al.); U.S. Pat. No. 4,744,802 (Schwabel),U.S. Pat. No. 4,770,671 (Monroe et al.); and U.S. Pat. No. 4,881,951(Monroe et al.).

In a preferred embodiment, the secondary abrasive particles are selectedfrom particles of fused oxide materials, including fused aluminum oxidematerials or fused alumina-zirconia, preferably fused aluminum oxide.

In another preferred embodiment, the secondary abrasive particles areselected from particles of superabrasive materials, for example cubicboron nitride and natural or synthetic diamond. Suitable diamond orcubic boron nitride materials can be crystalline or polycrystalline. Apreferred superabrasive material for use as secondary abrasive particlesis cubic boron nitride.

In yet another embodiment, the secondary abrasive particles are selectedfrom particles of silicon carbide materials.

The secondary abrasives particles comprised in the blend may have anabrasives industry specified nominal grade or a nominal screened grade.As mentioned, the shaped abrasive particles may also have an abrasiveindustry specified nominal grade or a nominal screened grade and thegrade(s) of the secondary abrasive particles and the grade(s) of theshaped abrasive particles of the present invention can be independentlyselected from any useful grade.

For example, the abrasive article may further comprise crushed abrasiveparticles (excluding abrasive shards as defined herein) which canoptionally correspond to an abrasive industry specified nominal gradedor combination thereof. The crushed abrasive particles can be of a finersize grade or grades (e.g., if a plurality of size grades are used) thanthe shaped abrasive particles. In some embodiments, the crushed abrasiveparticles can be of a coarser size grade or grades (e.g., if a pluralityof size grades are used) than the shaped abrasive particles.

Typically, conventional crushed abrasive particles are independentlysized according to an abrasives industry recognized specified nominalgrade. Exemplary abrasive industry recognized grading standards andgrades for secondary abrasive particles include those as mentioned withrespect to shaped abrasive particles.

Methods to provide shaped abrasive particles are known in the art andinclude technologies based on (1) fusion, (2) sintering, and (3)chemical ceramic. While preferred shaped abrasive particles can beobtained by using chemical ceramic technology, non-ceramic shapedabrasive particles are also included within the scope of the presentinvention. In the description of the invention, methods for preparingshaped abrasive particles may be described with specific reference toceramic shaped abrasive particles, particularly alumina based ceramicshaped abrasive particles. It is to be understood however that theinvention is not limited to alumina but is capable of being adapted foruse with a plurality of different hard and superhard materials.

The shaped abrasive particles used in the present invention cantypically be made using tools (i.e., molds), cut using diamond tooling,which provides higher feature definition than other fabricationalternatives such as, for example, stamping or punching. Typically, thecavities in the tool surface have planar faces that meet along sharpedges, and form the sides and top of a truncated pyramid. The resultantshaped abrasive particles have a respective nominal average shape thatcorresponds to the shape of cavities (e.g., truncated pyramid) in thetool surface; however, variations (e.g., random variations) from thenominal average shape may occur during manufacture, and shaped abrasiveparticles exhibiting such variations are included within the definitionof shaped abrasive particles as used herein.

Shaped abrasive particles (for example alpha-alumina based ceramicparticles) can be made according to a multistep process typically usinga dimensionally stable dispersion of a suitable precursor (for example aceramic precursor).

The dispersion that is typically employed in the process may be anydispersion of a suitable precursor and by this is intended a finelydispersed material that, after being subjected to a process suitable inthe invention, is in the form of a shaped abrasive particle. Theprecursor may be chemically a precursor, as for example boehmite is achemical precursor of alpha alumina; a morphological precursor as forexample gamma alumina is a morphological precursor of alpha alumina; aswell as (or alternatively), physically a precursor in the sense of thata finely divided form of alpha alumina can be formed into a shape andsintered to retain that shape. In typical cases, the dimensionallystable dispersion of a suitable precursor is a sol-gel.

Where the dispersion comprises a physical or morphological precursor asthe term is used herein, the precursor is in the form of finely dividedpowder grains that, when sintered together, form an abrasive particle ofutility in conventional bonded and coated abrasive applications. Suchmaterials generally comprise powder grains with an average size of lessthan about 20 microns, preferably less than about 10 microns and mostpreferably less than about a micron. The solids content of a dispersionof a physical or a morphological precursor is preferably from about 40to 65% though higher solids contents of up to about 80% can be used. Anorganic compound is frequently used along with the finely divided grainsin such dispersions as a suspending agent or perhaps as a temporarybinder until the particle has been dried sufficiently to maintain itsshape. This can be any of those generally known for such purposes suchas polyethylene glycol, sorbitan esters and the like.

The solids content of a chemical precursor that changes to its finalstable (for example, ceramic) form upon heating may need to take intoaccount water that may be liberated from the precursor during drying andfiring to sinter the particles. In such cases the solids content istypically somewhat lower such as about 75% or lower and more preferablybetween about 30% and about 50%. With a boehmite gel a maximum solidscontent of about 60% or even 40% is preferred and a gel with a peptizedminimum solids content of about 20% may also be used.

Particles made from physical precursors will typically need to be firedat higher temperatures than those formed from a seeded chemicalprecursor. For example, whereas particles of a seeded boehmite gel forman essentially fully densified alpha alumina at temperatures below about1250° C., particles made from alpha alumina gels require a firingtemperature of above about 1400° C. for full densification.

By way of example, a method suitable for use in the present inventioncomprises chemical ceramic technology involving converting a colloidaldispersion or hydrosol (sometimes called a sol), optionally in a mixturewith solutions of other metal oxide precursors, to a gel or any otherphysical state that restrains the mobility of the components, drying,and firing to obtain a ceramic material. A sol can be prepared by any ofseveral methods, including precipitation of a metal hydroxide from anaqueous solution followed by peptization, dialysis of anions from asolution of metal salt, solvent extraction of an anion from a solutionof a metal salt, hydrothermal decomposition of a solution of a metalsalt having a volatile anion. The sol optionally contains metal oxide orprecursor thereof and is transformed to a semi-rigid solid state oflimited mobility such as a gel by, e.g., partial extraction of thesolvent, e.g., water, the gel can be shaped by any convenient methodsuch as pressing, molding, or extruding, to provide a shaped abrasivegrain.

An exemplary method involving chemical ceramic technology comprises thesteps of making a dimensionally stable dispersion of a ceramic precursor(which may for example include either a seeded or non-seeded sol-gelalpha alumina precursor dispersion that can be converted into alphaalumina); filling one or more mold cavities having the desired outershape of the shaped abrasive particle with the dimensionally stabledispersion of a ceramic precursor, drying the stable dispersion of aceramic precursor to form precursor ceramic shaped abrasive particles;removing the precursor ceramic shaped abrasive particles from the moldcavities; calcining the precursor ceramic shaped abrasive particles toform calcined, precursor ceramic shaped abrasive particles, and thensintering the calcined, precursor ceramic shaped abrasive particles toform ceramic shaped abrasive particles. The process is described in moredetail in U.S. Pat. No. 5,201,916 (Berg et al.).

The materials that can be made into shaped particles of the inventioninclude physical precursors such as finely divided particles of knownceramic materials, carbides, nitrides such as alpha alumina, tungstencarbide, silicon carbide, titanium nitride, alumina/zirconia and cubicboron nitride (CBN). Also included are chemical and/or morphologicalprecursors such as aluminum trihydrate, boehmite, gamma alumina andother transitional aluminas and bauxite. The most useful of the aboveare typically based on alumina, and its physical or chemical precursorsand in the specific descriptions that follow a method suitable for usein the invention is illustrated with specific reference to alumina.

Other components that have been found to be desirable in certaincircumstances for the production of alumina-based particles includenucleating agents such as finely divided alpha alumina, ferric oxide,chromium oxide and other materials capable of nucleating thetransformation of precursor faints to the alpha alumina form; oxides ofmagnesium; titanium; zirconium; yttrium; and other rare earth metaloxides. Such additives often act as crystal growth limiters or boundaryphase modifiers. The amount of such additives in the precursor isusually less than about 10% and often less than 5% by weight (solidsbasis).

It is also possible to use, instead of a chemical or morphologicalprecursor of alpha alumina, a slip of finely divided alpha aluminaitself together with an organic compound that will maintain it insuspension and act as a temporary binder while the particle is beingfired to essentially full densification. In such cases it is oftenpossible to include in the suspension materials that will form aseparate phase upon firing or that can act as an aid in maintaining thestructural integrity of the shaped particles either during drying andfiring, or after firing. Such materials may be present as impurities. Iffor example the precursor is finely divided bauxite, there will be asmall proportion of vitreous material present that will form a secondphase after the powder grains are sintered together to form the shapedparticle.

Ceramic shaped abrasive particles composed of crystallites of alphaalumina, magnesium alumina spinel, and a rare earth hexagonal aluminatemay also be used. Such particles may be prepared using sol-gel precursoralpha alumina particles according to methods described in, for example,U.S. Pat. No. 5,213,591 (Celikkaya et al.) and U.S. Publ. Patent Appl.Nos. 2009/0165394 A1 (Culler et al.) and 2009/0169816 A1 (Erickson etal.).

In some embodiments, ceramic shaped abrasive particles can be madeaccording to a multistep process. The process will now be described ingreater detail with specific reference to alumina. Generally, alphaalumina based shaped abrasive particles can be made from a dispersion ofaluminum oxide monohydrate that is gelled, molded to shape, dried toretain the shape, calcined, and sintered as is known in the art. Theshaped abrasive particle's shape is retained without the need for abinder.

The first process step of the multi-step process involves providingeither a seeded or non-seeded dispersion of an alpha alumina precursorthat can be converted into alpha alumina. The alpha alumina precursordispersion often comprises a liquid that is a volatile component. In oneembodiment, the volatile component is water. The dispersion shouldcomprise a sufficient amount of liquid for the viscosity of thedispersion to be sufficiently low to enable filling mold cavities andreplicating the mold surfaces, but not so much liquid as to causesubsequent removal of the liquid from the mold cavity to beprohibitively expensive. In one embodiment, the alpha alumina precursordispersion comprises from 2 percent to 90 percent by weight of theparticles that can be converted into alpha alumina, such as particles ofaluminum oxide monohydrate (boehmite), and at least 10 percent byweight, or from 50 percent to 70 percent, or 50 percent to 60 percent,by weight of the volatile component such as water. Conversely, the alphaalumina precursor dispersion in some embodiments contains from 30percent to 50 percent, or 40 percent to 50 percent, by weight solids.

Aluminum oxide hydrates other than boehmite can also be used. Boehmitecan be prepared by known techniques or can be obtained commercially.Examples of commercially available boehmite include products having thetrade designations “DISPERAL”, and “DISPAL”, both available from SasolNorth America, Inc, of Houston, Tex., or “HiQ-40” available from BASFCorporation of Florham Park, N.J. These aluminum oxide monohydrates arerelatively pure; that is, they include relatively little, if any,hydrate phases other than monohydrates, and have a high surface area.

The physical properties of the resulting ceramic shaped abrasiveparticles will generally depend upon the type of material used in thealpha alumina precursor dispersion. In one embodiment, the alpha aluminaprecursor dispersion is in a gel state. As used herein, a “gel” is athree-dimensional network of solids dispersed in a liquid.

The alpha alumina precursor dispersion may contain a modifying additiveor precursor of a modifying additive. The modifying additive canfunction to enhance some desirable property of the abrasive particles orincrease the effectiveness of the subsequent sintering step.

Modifying additives or precursors of modifying additives can be in theform of soluble salts, typically water soluble salts. They typicallyconsist of a metal-containing compound and can be a precursor of oxideof magnesium, zinc, iron, silicon, cobalt, nickel, zirconium, hafnium,chromium, yttrium, praseodymium, samarium, ytterbium, neodymium,lanthanum, gadolinium, cerium, dysprosium, erbium, titanium, andmixtures thereof. The particular concentrations of these additives thatcan be present in the alpha alumina precursor dispersion can be variedbased on skill in the art.

Typically, the introduction of a modifying additive or precursor of amodifying additive will cause the alpha alumina precursor dispersion togel. The alpha alumina precursor dispersion can also be induced to gelby application of heat over a period of time. The alpha aluminaprecursor dispersion can also contain a nucleating agent (seeding) toenhance the transformation of hydrated or calcined aluminum oxide toalpha alumina. Nucleating agents suitable for this invention includefine particles of alpha alumina, alpha ferric oxide or its precursor,titanium oxides and titanates, chrome oxides, or any other material thatwill nucleate the transformation. The amount of nucleating agent, ifused, should be sufficient to effect the transformation of alphaalumina. Nucleating such alpha alumina precursor dispersions isdisclosed in U.S. Pat. No. 4,744,802 (Schwabel).

A peptizing agent can be added to the alpha alumina precursor dispersionto produce a more stable hydrosol or colloidal alpha alumina precursordispersion. Suitable peptizing agents are monoprotic acids or acidcompounds such as acetic acid, hydrochloric acid, formic acid, andnitric acid. Multiprotic acids can also be used but they can rapidly gelthe alpha alumina precursor dispersion, making it difficult to handle orto introduce additional components thereto. Some commercial sources ofboehmite contain an acid titer (such as absorbed formic or nitric acid)that will assist in forming a stable alpha alumina precursor dispersion.

The alpha alumina precursor dispersion can be formed by any suitablemeans, such as, for example, by simply mixing aluminum oxide monohydratewith water containing a peptizing agent or by forming an aluminum oxidemonohydrate slurry to which the peptizing agent is added.

Defoamers or other suitable chemicals can be added to reduce thetendency to form bubbles or entrain air while mixing. Additionalchemicals such as wetting agents, alcohols, or coupling agents can beadded if desired. The alpha alumina abrasive particles may containsilica and iron oxide as disclosed in U.S. Pat. No. 5,645,619 (Ericksonet al.). The alpha alumina abrasive particles may contain zirconia asdisclosed in U.S. Pat. No. 5,551,963 (Larmie). Alternatively, the alphaalumina abrasive particles can have a microstructure or additives asdisclosed in U.S. Pat. No. 6,277,161 (Castro).

The second process step involves providing a mold having at least onemold cavity, and preferably a plurality of cavities. The mold can have agenerally planar bottom surface and a plurality of mold cavities. Theplurality of cavities can be formed in a production tool. The productiontool can be a belt, a sheet, a continuous web, a coating roll such as arotogravure roll, a sleeve mounted on a coating roll, or die. In oneembodiment, the production tool comprises polymeric material. Examplesof suitable polymeric materials include thermoplastics such aspolyesters, polycarbonates, poly(ether sulfone), poly(methylmethacrylate), polyurethanes, polyvinylchloride, polyolefin,polystyrene, polypropylene, polyethylene or combinations thereof, orthermosetting materials. In one embodiment, the entire tooling is madefrom a polymeric or thermoplastic material. In another embodiment, thesurfaces of the tooling in contact with the sol-gel while drying, suchas the surfaces of the plurality of cavities, comprises polymeric orthermoplastic materials and other portions of the tooling can be madefrom other materials. A suitable polymeric coating may be applied to ametal tooling to change its surface tension properties by way ofexample.

A polymeric or thermoplastic tool can be replicated off a metal mastertool. The master tool will have the inverse pattern desired for theproduction tool. The master tool can be made in the same manner as theproduction tool. In one embodiment, the master tool is made out ofmetal, e.g., nickel and is diamond turned. The polymeric sheet materialcan be heated along with the master tool such that the polymericmaterial is embossed with the master tool pattern by pressing the twotogether. A polymeric or thermoplastic material can also be extruded orcast onto the master tool and then pressed. The thermoplastic materialis cooled to solidify and produce the production tool. If athermoplastic production tool is utilized, then care should be taken notto generate excessive heat that may distort the thermoplastic productiontool limiting its life. More information concerning the design andfabrication of production tooling or master tools can be found in U.S.Pat. No. 5,152,917 (Pieper et al.); U.S. Pat. No. 5,435,816 (Spurgeon etal.); U.S. Pat. No. 5,672,097 (Hoopman et al.); U.S. Pat. No. 5,946,991(Hoopman et al.); U.S. Pat. No. 5,975,987 (Hoopman et al.); and U.S.Pat. No. 6,129,540 (Hoopman et al.).

Access to cavities can be from an opening in the top surface or bottomsurface of the mold. In some instances, the cavities can extend for theentire thickness of the mold. Alternatively, the cavities can extendonly for a portion of the thickness of the mold. In one embodiment, thetop surface is substantially parallel to bottom surface of the mold withthe cavities having a substantially uniform depth. At least one side ofthe mold, that is, the side in which the cavities are formed, can remainexposed to the surrounding atmosphere during the step in which thevolatile component is removed.

The cavities have a specified three-dimensional shape to make theceramic shaped abrasive particles. The depth dimension is equal to theperpendicular distance from the top surface to the lowermost point onthe bottom surface. The depth of a given cavity can be uniform or canvary along its length and/or width. The cavities of a given mold can beof the same shape or of different shapes.

The third process step involves filling the cavities in the mold withthe alpha alumina precursor dispersion (e.g., by a conventionaltechnique). In some embodiments, a knife roll coater or vacuum slot diecoater can be used. A mold release can be used to aid in removing theparticles from the mold if desired. Typical mold release agents includeoils such as peanut oil or mineral oil, fish oil, silicones,polytetrafluoroethylene, zinc stearate, and graphite. In general, moldrelease agent such as peanut oil, in a liquid, such as water or alcohol,is applied to the surfaces of the production tooling in contact with thesol-gel such that between about 0.1 mg/in² (0.02 mg/cm²) to about 3.0mg/in² 0.46 mg/cm²), or between about 0.1 mg/in² (0.02 mg/cm²) to about5.0 mg/in² (0.78 mg/cm²) of the mold release agent is present per unitarea of the mold when a mold release is desired. In some embodiments,the top surface of the mold is coated with the alpha alumina precursordispersion. The alpha alumina precursor dispersion can be pumped ontothe top surface.

Next, a scraper or leveler bar can be used to force the alpha aluminaprecursor dispersion fully into the cavity of the mold. The remainingportion of the alpha alumina precursor dispersion that does not entercavity can be removed from top surface of the mold and recycled. In someembodiments, a small portion of the alpha alumina precursor dispersioncan remain on the top surface and in other embodiments the top surfaceis substantially free of the dispersion. The pressure applied by thescraper or leveler bar is typically less than 100 psi (0.7 MPa), lessthan 50 psi (0.3 MPa), or even less than 10 psi (69 kPa). In someembodiments, no exposed surface of the alpha alumina precursordispersion extends substantially beyond the top surface to ensureuniformity in thickness of the resulting ceramic shaped abrasiveparticles.

The fourth process step involves removing the volatile component to drythe dispersion. Desirably, the volatile component is removed by fastevaporation rates. In some embodiments, removal of the volatilecomponent by evaporation occurs at temperatures above the boiling pointof the volatile component. An upper limit to the drying temperatureoften depends on the material the mold is made from. For polypropylenetooling the temperature should be less than the melting point of theplastic. In one embodiment, for a water dispersion of between about 40to 50 percent solids and a polypropylene mold, the drying temperaturescan be between about 90° C. to about 165° C., or between about 105° C.to about 150° C., or between about 105° C. to about 120° C. Highertemperatures can lead to improved production speeds but can also lead todegradation of the polypropylene tooling limiting its useful life as amold.

The fifth process step involves removing resultant precursor ceramicshaped abrasive particles from the mold cavities. The precursor ceramicshaped abrasive particles can be removed from the cavities by using thefollowing processes alone or in combination on the mold: gravity,vibration, ultrasonic vibration, vacuum, or pressurized air to removethe particles from the mold cavities.

The precursor abrasive particles can be further dried outside of themold. If the alpha alumina precursor dispersion is dried to the desiredlevel in the mold, this additional drying step is not necessary.However, in some instances it may be economical to employ thisadditional drying step to minimize the time that the alpha aluminaprecursor dispersion resides in the mold. Typically, the precursorceramic shaped abrasive particles will be dried from 10 to 480 minutes,or from 120 to 400 minutes, at a temperature from 50° C. to 160° C., orat 120° C. to 150° C.

The sixth process step involves calcining the precursor ceramic shapedabrasive particles. During calcining, essentially all the volatilematerial is removed, and the various components that were present in thealpha alumina precursor dispersion are transformed into metal oxides.The precursor ceramic shaped abrasive particles are generally heated toa temperature from 400° C. to 800° C., and maintained within thistemperature range until the free water and over 90 percent by weight ofany bound volatile material are removed. In an optional step, it may bedesired to introduce the modifying additive by an impregnation process.A water-soluble salt can be introduced by impregnation into the pores ofthe calcined, precursor ceramic shaped abrasive particles. Then theprecursor ceramic shaped abrasive particles are pre-fired again. Thisoption is further described in U.S. Pat. No. 5,164,348 (Wood).

The seventh process step involves sintering the calcined, precursorceramic shaped abrasive particles to form alpha alumina particles. Priorto sintering, the calcined, precursor ceramic shaped abrasive particlesare not completely densified and thus lack the desired hardness to beused as ceramic shaped abrasive particles. Sintering takes place byheating the calcined, precursor ceramic shaped abrasive particles to atemperature of from 1000° C. to 1650° C. and maintaining them withinthis temperature range until substantially all of the alpha aluminamonohydrate (or equivalent) is converted to alpha alumina and theporosity is reduced to less than 15 percent by volume. The length oftime to which the calcined, precursor ceramic shaped abrasive particlesmust be exposed to the sintering temperature to achieve this level ofconversion depends upon various factors but usually from five seconds to48 hours is typical.

In another embodiment, the duration for the sintering step ranges fromone minute to 90 minutes. After sintering, the ceramic shaped abrasiveparticles can have a Vickers hardness of 10 GPa, 16 GPa, 18 GPa, 20 GPa,or greater.

Other steps can be used to modify the described process such as, forexample, rapidly heating the material from the calcining temperature tothe sintering temperature, centrifuging the alpha alumina precursordispersion to remove sludge and/or waste. Moreover, the process can bemodified by combining two or more of the process steps if desired.Conventional process steps that can be used to modify the process ofthis disclosure are more fully described in U.S. Pat. No. 4,314,827(Leitheiser). More information concerning methods to make ceramic shapedabrasive particles is disclosed in US Patent Application Publication No.2009/0165394 A1 (Culler et al.).

Methods for making shaped abrasive particles having at least one slopingsidewall are for example described in US Patent Application PublicationNos. 2010/0151196 and 2009/0165394. Methods for making shaped abrasiveparticles having an opening are for example described in US PatentApplication Publication No. 2010/0151201 and 2009/0165394. Methods formaking shaped abrasive particles having grooves on at least one side arefor example described in US Patent Application Publication No.2010/0146867. Methods for making dish-shaped abrasive particles are forexample described in US Patent Application Publication Nos. 2010/0151195and 2009/0165394. Methods for making shaped abrasive particles with lowRoundness Factor are for example described in US Patent ApplicationPublication No. 2010/0319269. Methods for making shaped abrasiveparticles with at least one fractured surface are for example describedin US Patent Application Publication Nos. 2009/0169816 and 2009/0165394.Methods for making abrasive particles wherein the second side comprisesa vertex (for example, dual tapered abrasive particles) or a ridge line(for example, roof shaped particles) are for example described in WO2011/068714.

The bonding medium of a bonded abrasive article serves to retain theshaped abrasive particles (and any optional components, such assecondary abrasive particles, fillers and additives) in the abrasivearticle. According to the present invention, the bonding mediumcomprises a vitreous (also referred to as vitrified) bond phase. In apreferred embodiment, the bonding medium is a vitreous bond (phase). Thevitreous bond serves to retain the shaped abrasive particles (and anyoptional secondary abrasive particles as described herein) in thearticle. The vitreous bond phase which binds together the abrasiveparticles (shaped abrasive particle and any optional secondary abrasiveparticles) can be of any suitable composition.

The vitreous bond phase, also known in the art as a “vitrified bond”,“vitreous bond”, “ceramic bond” or “glass bond”, may be produced from avitreous bond precursor composition comprising a mixture or combinationof one or more raw materials that when heated to a high temperature meltand/or fuse to form an integral vitreous matrix phase. Typical rawmaterials for forming a vitreous bond phase can be selected from metaloxides (including metalloid oxides), non-metal oxides, non-metalcompounds, silicates and naturally occurring and synthetic minerals, andcombinations of one or more of these raw materials.

Metal oxides can for example be selected from silicon oxide, aluminiumoxide, magnesium oxide, calcium oxide, barium oxide, lithium oxide,sodium oxide, potassium oxide, iron oxide, titanium oxide, manganeseoxide, zinc oxide, and metal oxides that can be characterized aspigments such as cobalt oxide, chromium oxide, or iron oxide, andcombinations thereof.

Non-metal oxides can for example be selected from boron oxide orphosphorous oxide and combinations thereof.

Suitable examples for non-metal compounds include boric acid.

Silicates can for example be selected from aluminum silicates,borosilicates, calcium silicates, magnesium silicates, sodium silicates,magnesium silicates, lithium silicates, and combinations thereof.

Minerals can for example be selected from clay, feldspar, kaolin,wollastonite, borax, quartz, soda ash, limestone, dolomite, chalk, andcombinations thereof.

In the present invention, the vitreous bond phase may also be formedfrom a frit, i.e. a composition that has been prefired prior to itsemployment in a vitreous bond precursor composition for forming thevitreous bond phase of a bonded abrasive article. As used herein, theterm “fit” is a generic term for a material that is formed by thoroughlyblending a mixture comprising one or more frit forming components,followed by heating (also referred to as prefixing) the mixture to atemperature at least high enough to melt it; cooling the glass andpulverizing it. The frit forming components are usually mixed togetheras powders, fired to fuse the mixture and then the fused mixture iscooled. The cooled mixture is crushed and screened to a fine powder tothen be used as a frit bond. The fineness of the powder is notparticularly limited. Examples of illustrative particle sizes includebut are not limited to particle sizes of ≦35 μm or ≦63 μm. It is thisfinal powder that may be used in a vitreous bond precursor compositionto prepare the vitreous bond of a bonded abrasive article of theinvention, such as a grinding wheel.

Frits, their sources and compositions are well known in the art. Fritforming components include materials which have been previously referredto as raw materials for forming a vitreous bond. Frits are well knownmaterials and have been used for many years as enamels for coating, forexample, porcelain, metals and jewellery, but also for vitreous bonds oftechnical ceramics and grinding wheels. Frits as well as ceramic bondsfor vitrified bonded abrasive articles are commercially available fromsuppliers such as Ferro Corporation, 1000 Lakeside Avenue, Cleveland,Ohio, USA 44114-7000 and Reimbold & Strick, Cologne, Germany. Frits forthe use in vitrified bonded abrasive articles typically show meltingtemperatures in the range of 500 to 1300° C.

In accordance with the present invention, frits may be used in additionto the raw materials or in lieu of the raw materials. Alternatively, thevitreous bond may be derived from a non-frit containing composition.

For example, a vitreous bond can be formed from a vitreous bondprecursor composition comprising from more than 0 to 100% by weightfrit, although more typically the composition comprises 3 to 70% frit.The remaining portion of the vitreous bond precursor composition can bea non-fit material.

Suitable ranges for vitrified bond compositions can be specified asfollows: 25 to 90% by weight, preferably 35 to 85% by weight, based onthe total weight of the vitreous bond, of SiO₂; 0 to 40% by weight,preferably 0 to 30% by weight, based on the total weight of the vitreousbond, of B₂O₃; 0 to 40% by weight, preferably 5 to 30% by weight, basedon the total weight of the vitreous bond, of Al₂O₃; 0 to 5% by weight,preferably 0 to 3% by weight, based on the total weight of the vitreousbond, of Fe₂O₃, 0 to 5% by weight, preferably 0 to 3% by weight, basedon the total weight of the vitreous bond, of TiO₂, 0 to 20% by weight,preferably 0 to 10% by weight, based on the total weight of the vitreousbond, of CaO; 0 to 20% by weight, preferably 0 to 10% by weight, basedon the total weight of the vitreous bond, of MgO; 0 to 20% by weight,preferably 0 to 10% by weight, based on the total weight of the vitreousbond, of K₂O; 0 to 25% by weight, preferably 0 to 15% by weight, basedon the total weight of the vitreous bond, of Na₂O; 0 to 20% by weight,preferably 0 to 12% by weight, based on the total weight of the vitreousbond, of Li₂O; 0 to 10% by weight, preferably 0 to 3% by weight, basedon the total weight of the vitreous bond, of ZnO; 0 to 10% by weight,preferably 0 to 3% by weight, based on the total weight of the vitreousbond, of BaO; and 0 to 5% by weight, preferably 0 to 3% by weight, basedon the total weight of the vitreous bond, of metallic oxides [e.g. CoO,Cr₂O₃ (pigments)].

It is known in the art to use various additives in the making ofvitreous bonded abrasive articles both to assist in the making of theabrasive article and/or improve the performance of such articles. Suchconventional additives which may also be used in the practice of thisinvention include but are not limited to lubricants, fillers, temporarybinders and processing aids.

Organic binders are preferably used as temporary binders. Typicaltemporary binders are dextrins, urea resins (including urea formaldehyderesins), polysaccharides, polyethylene glycol, polyacrylates, and anyother types of glue etc. These binders may also include a liquidcomponent, such as water or polyethylene glycol, viscosity or pHmodifiers and mixing aids. The use of temporary binders may improvehomogeneity and the structural quality of the pre-fired or green pressedbody as well as of the fired article. Because the binders are burned outduring firing, they do not become part of the finished bond or abrasivearticle.

Bonded abrasive articles according to the present invention can be madeaccording to any suitable method. Procedures and conditions well knownin the art for producing vitrified bonded abrasive articles (e.g.,grinding wheels) and especially procedures and conditions for producingvitreous bonded sol-gel alumina-based abrasive articles may be used tomake the abrasive article of this invention. These procedures may employconventional and well known equipment in the art.

An exemplary method for manufacturing a bonded abrasive article of theinvention comprises the steps of:

-   -   (a) providing a precursor composition comprising shaped abrasive        particles in accordance with the present invention and a        vitreous bond precursor composition and optionally one or more        components selected from a temporary binder composition        (including for example one or more components selected from one        or more temporary binder(s) and pore inducing agent(s)) and        secondary abrasive particles;    -   (b) forming the precursor composition to a desired shape so as        to obtain a green structure;    -   (c) optionally, drying the green structure;    -   (d) firing the green structure obtained in step (b) or (c) at        temperatures suitable to produce a vitreous bond (for example at        temperatures selected from about 700° C. to about 1500° C.) so        as to obtain a vitrified bonded abrasive article having a first        shape (for example a straight wheel shape, e.g., T1 type);    -   (e) optionally, further altering the first shape in one or more        shape features (for example bore, diameter, thickness, face        profile) so as to obtain a bonded abrasive article having a        second shape (for example a shape resulting from customer        needs).

For example, during manufacture of a vitrified bonded abrasive article,the vitreous bond precursor composition, in a powder form, may be mixedwith a temporary binder (typically an organic binder) which does notform part of the fired vitrified bonding medium. Bonded abrasivearticles are typically prepared by forming a green structure comprisedof abrasive grain, the vitreous bond precursor composition, andoptionally, a temporary binder and other optional additives and fillers.Forming can for example be accomplished by molding with or withoutpressing. Typical forming pressures can vary within wide ranges and maybe selected from pressures ranging from 0 to 400 kg/cm², depending onthe composition of the green structure. The green structure is thenfired. The vitreous bond phase is usually produced in the firing step,typically at a temperature(s) in the range from about 700° C. to about1500° C., preferably in the range from about 750° C. to about 1350° C.and most preferably in the range from about 800° C. to about 1300° C.Good results may be also obtained at temperatures of about 1000° C. orless, or from about 1100 to about 1200° C. The actual temperature atwhich the vitreous bond phase is formed depends, for example, on theparticular bond chemistry. Firing of the vitreous bond precursorcomposition is typically accomplished by raising the temperature fromroom temperature to the maximum temperature over a prolonged period oftime (e.g., about 10-130 hours), holding at the maximum temperature,e.g., for 1-20 hours, and then cooling the fired article to roomtemperature over an extended period of time, e.g., 10-140 hours. Itshould be understood that the temperature selected for the firing stepand the composition of the vitreous bond phase must be chosen so as tonot have a detrimental effect on the physical properties and/orcomposition of the abrasive particles (shaped and optional secondaryparticles) contained in the abrasive article.

A bonded abrasive article according to the present invention comprisesshaped abrasive particles (as defined in accordance with the presentinvention) and a bonding medium comprising a vitreous bond. In addition,the bonded abrasive article may comprise one or more optional componentsselected from secondary abrasive particles, fillers and additives.

The amounts of abrasive particles (which may be comprised in a blendincluding one or more secondary abrasive particles) may vary widely andcan range for example from 10 to 80%, more preferably from 25 to 60% byvolume.

While the invention has a most pronounced effect when the abrasivefraction (or blend) includes 100% by weight of shaped abrasive particlesin accordance with the present invention based on the total weight ofabrasive particles present in the abrasive fraction (or blend), it isalso effective when the article contains for example as little as 5% byweight of shaped abrasive particles in accordance with the presentinvention and up to 95% by weight of secondary abrasive particles, basedon the total weight of abrasive particles present in the abrasivefraction. Hence, the abrasive article can contain a total amount ofabrasive particles of up to 100% by weight of the abrasive particlesaccording to this invention, based on the total weight of abrasiveparticles. In some embodiments, the bonded abrasive article can includefrom about 5 to 100, preferably 10 to 80 percent by weight of shapedabrasive particles; typically 20 to 60 percent by weight, and moretypically 30 to 50 percent by weight, based on the total weight ofabrasive particles. In some grinding applications the addition of asecondary abrasive particle is for the purpose of reducing the cost ofthe abrasive article by reducing the amount of premium priced shapedabrasive particles. In other applications a mixture with a secondaryabrasive particle may have a synergistic effect.

The amount of bonding medium may also vary widely and can range forexample from 1 to 60% by volume, more preferably 2.5 to 40% by volume.

Optionally, the bonded abrasive article can comprise porosity. Bondedabrasive articles containing porosity have an open structure(interlinked or interconnected porosity) which can provide chipclearance for high material removal, transport more coolant into thecontact area while decreasing friction, and optimizes theself-sharpening process. Porosity enables the bonded abrasive article toshed used or worn abrasive particles to expose new cutting edges orfresh abrasive particles.

Bonded abrasive articles according to the present invention can have anyuseful range of porosity; such as from about 5 to about 80% by volume,preferably from about 20 to about 70% by volume.

Preferably, the bonded abrasive article according to the presentinvention contains porosity. The porosity can be formed by the naturalspacing provided by the packing density of the materials comprised inthe bonded abrasive articles and by pore inducing components, as knownin the art, or by both.

Pore inducing components can be selected from temporary components (i.e.components not present in the final article) non-temporary components(i.e. (components present in the final article) and combinationsthereof. Preferred pore inducing components should not leave anychemical traces in a finished abrasive article (i.e. be temporarycomponents), do not expand upon removal, mix well with the abrasiveparticles and can provide the desired type (e.g. interconnected) andextent of porosity. Pore inducing components are typically used inamounts ranging from 0-40 Vol.-% of the total article. Typicalnon-temporary pore inducing components may be selected from materialssuch as hollow spheres made of materials such as glass, ceramic(aluminium oxide) and glass particles. Typical temporary pore inducingcomponents may be selected from materials such as polymeric materials(including foamed polymeric materials) cork, ground walnut shells, woodparticles, organic compounds (such as naphthalene or paradichlorbenzene)and combinations thereof. In a preferred embodiment, the abrasivearticle contains porosity induced by using naphthalene (as a temporarypore inducing component).

Bonded abrasive articles according to the present invention may containadditional components such as, for example, fillers and additives, as isknown in the art. Examples of optional additives contained in the bondedabrasive article include non-temporary pore inducing agents, asdescribed in the foregoing, and any components used when making thevitreous bond, including but not limited to lubricants, fillers,temporary binders and processing aids.

Bonded abrasive articles in accordance with the present invention have athree-dimensional shape, which is not particularly limited. Typically,the shape of a bonded abrasive article according to the invention isselected depending on factors such as the intended grinding application(including grinding method, grinding conditions and workpiece) as wellas customer needs.

By way of exemplification, International Standard ISO 603:1999 listssuitable shapes of bonded abrasive articles all of which are useful inthe present invention. Standard types according to standards of FEPA(Federation of European Producers of Abrasives) or other standards aswell as non-standard types can also be used.

By way of illustration, typical shapes can for example include but arenot limited to the shape of a wheel, honing stone, grinding segment,mounted point or other types according to standard forms of FEPA or ISO603:1999 and other standards as well as non-standard individual types.

A preferred bonded abrasive article is a vitrified bonded abrasivewheel, in particular, a vitrified bonded grinding wheel.

The diameter of abrasive wheels in accordance with the present inventionis not particularly limited and can for example be selected to rangefrom 1 ram to 2000 mm, or from 10 mm to 1200 mm or from 100 mm to 750mm, although other dimensions may also be used. Likewise, the thicknessof abrasive (grinding) wheels is not particularly limited. For example,the thickness can typically be selected to range from 2 to 600 mm, orfrom 5 to 350 mm, or from 10 mm to 300 mm, although other dimensions mayalso be used. For example, a bore diameter may range from 0 mm to 800mm, more typically from 4 mm to 400 or from 8 mm to 350 mm.

The particular design of the abrasive article (preferably grindingwheel) is not limited and can be selected from “monolithic” designs and“zonal” design (such as segmented and layered designs). Both designs caninclude the reinforcement of the bore by using glues such asthermosetting resins, for example resins selected from epoxy resins,polycondensates, and phenolic resins.

The abrasive particles (i.e. one or more type of shaped abrasiveparticles and optionally one or more types of secondary abrasiveparticles) may be homogeneously or non-homogeneously distributed in theabrasive article, for example be distributed or concentrated in selectedareas, layers, segments or portions of the abrasive article. Homogeneousor non-homogeneous distribution may be either as a homogeneous blend orin a way that different types of abrasive particles are located anddistributed only in selected areas, layers, segments or portions of theabrasive article.

For example, a bonded abrasive wheel, may comprise at least two distinctsections, including an outer zone (also often referred to as rim orperiphery) and an inner zone (also often referred to as core or centerportion). The distinct sections may be provided based on differences inone or more aspects selected from the composition of the bond (forexample the type of bonding material or the amount of porosity present),the shape of abrasive particles (for example shaped versus crushed orfirst shape versus second shape), the grit size of abrasive particle(for example, finer versus coarser) and the amount of abrasive particles(for example presence or absence of abrasive particles or first (forexample high) amount versus second (for example low) amount).

In some embodiments the outer zone comprises shaped abrasive particlesaccording to the present invention whereas the inner zone does not.

In other embodiments, the inner zone comprises shaped abrasive particlesaccording to the present invention whereas the outer zone does not.

An abrasive wheel may also contain an inner zone made of a non-vitreousbonding material (such as plastics etc.).

If the bonded abrasive article is an abrasive wheel, such as a grindingwheel, the abrasive particles may be concentrated towards the middle, oronly in the outer zone, i.e., the periphery, of the wheel. The centerportion may contain a different (higher or lower) amount of abrasiveparticles.

Another example for a zonal design is an abrasive wheel, such as agrinding wheel, having a rim containing shaped abrasive particles inaccordance with the present invention and an inner zone optionallycontaining and preferably not containing shaped abrasive particles inaccordance with the present invention. The inner zone of this design mayoptionally contain secondary abrasive particles (e.g, fused alumina,sintered alumina) that may have the same or different grit size. Thisdesign is also referred to as special centre design which is intended tominimize the grinding wheel costs due to the lack of shaped abrasiveparticles and at the same time to increase the bursting speed.

In another variation, an abrasive wheel may include two or more types ofabrasive particles positioned on different sides of the abrasive wheel.For example, first abrasive particles may be on one side of the wheelwith different abrasive particles on the opposite side. Either the firstor the second abrasive particles or both are selected from shapedabrasive particles in accordance with the present invention. However,typically all the abrasive particles are homogenously distributed amongeach other, because the manufacture of the wheels is easier, and thegrinding effect is optimized when the abrasive particles or the two ormore types thereof are closely positioned to each other.

In one embodiment, abrasive particles according to the present inventionare homogeneously distributed throughout the bonded abrasive article.

The present invention also relates to a method for abrading a workpiece,the method comprising frictionally contacting at least a portion of anabrasive article in accordance with the invention with a surface of aworkpiece; and moving (for example rotating) at least one of theworkpiece or the abrasive article to abrade at least a portion of thesurface of the workpiece.

The bonded abrasive articles of this invention can be advantageouslyused in a wide range of grinding applications.

Beneficial effects may be in particular achieved in grindingapplications which involve high material removal rates, in particulargrinding applications selected from roughing and semi-roughingoperations, i.e. applications typically involving high material removalrates.

The present invention is however not limited to grinding applicationswhich involve high material removal rates but may also be beneficiallyused in grinding applications which do not involve high material removalrates, such as finishing operations.

Hence, the bonded abrasive articles of this invention can be suitablyused in a wide range of grinding applications ranging from roughingoperations via semi-roughing to finishing operations.

Exemplary grinding applications include but are not limited tostandardized and non-standardized grinding applications, for examplemethods according to DIN-8589:2003.

The bonded abrasive articles of this invention are particularly suitablefor applications including but not limited to cylindrical grinding(outer diameter or OD grinding as well as internal diameter or IDgrinding), centerless grinding, gear grinding, generating gear grinding,surface and profile grinding, reciprocating grinding, creep-feedgrinding, grinding in generating method as well as by other methods ofgears, threads, tools, camshafts, crankshafts, bearings, guard rails,etc. Cut-off operations are less preferred but included within the scopeof the present invention. Preferred applications include gear grinding,creep-feed grinding, surface grinding, profile grinding, reciprocatinggrinding, grinding in generating method, cylindrical grinding (OD and IDgrinding) and centerless grinding, and particularly preferredapplications include cylindrical grinding applications, gear grindingapplications, surface grinding applications and particularlycreep-feed-grinding applications. The applied force during abrading isnot particularly limited and can be selected on the basis of thegrinding application.

During use, the bonded abrasive article can be used dry or wet. Duringwet grinding, the bonded abrasive article is typically used inconjunction with a grinding fluid which may for example contain water orcommercially available lubricants (also referred to as coolants). Duringwet grinding lubricants are commonly used to cool the workpiece andwheel, lubricate the interface, remove swarf (chips), and clean thewheel. The lubricant is typically applied directly to the grinding areato ensure that the fluid is not carried away by the grinding wheel. Thetype of lubrication used depends on the workpiece material and can beselected as is known in the art.

Common lubricants can be classified based on their ability to mix withwater. A first class suitable for use in the present invention includesoils, such as mineral oils (typically petroleum based oils) and plantoils. A second class suitably for use in the present invention includesemulsions of lubricants (for example mineral oil based lubricants; plantoil based lubricants and semi-synthetic lubricants) and solutions oflubricants (typically semi-synthetic and synthetic lubricants) withwater.

Abrasive articles in accordance with the present invention can be usedon any grinding machine specific for the grinding method The grindingmachine can be electrically, hydraulically or pneumatically driven, atany suitable speed, generally at speeds from about 10 to 250 m/s.

Bonded abrasive articles according to the present invention are useful,for example, for abrading a workpiece. The bonded abrasive article canbe particularly suitable for use on workpieces made of metal, such assteel (including powder metallurgical steel and steel alloys, carbonsteels, mild steels, tool steels, stainless steel, hardened steel, ballbearing steel, cold working steel, cast iron), non-ferrous metals andalloys (such as aluminum, titanium, bronze, etc.), hard metals (such astungsten carbide, titanium carbide, titanium nitride, cenimets, etc),ceramics (technical ceramics such as oxide ceramics, silicate ceramics,non-oxide ceramics), and glasses. The use of the bonded abrasivearticles is however not restricted to the use on these exemplifiedworkpiece materials.

Preferred grinding methods according to the present invention includebut are not limited to cylindrical grinding applications, gear grindingapplications and surface grinding applications including creep feedgrinding applications.

Gear Grinding

The term gear grinding as used in the present invention generally refersto a method of generative grinding and profile grinding of gears. Gearwheels determine the transmission ratios of gearboxes; according to thesecond fundamental law of gearing, this ratio will only remain constantif the next tooth is already engaged before the previous toothdisengages. The more perfectly ground the surface of the tooth flanks,the better is the form fit, and the more smoothly and quietly thegearbox runs. The process of machining the tooth flanks brings with ittough demands in terms of dimensional accuracy and shape accuracy—andalso places tough demands particularly on the edge zone properties ofthe component. Whereas very slight deviations in terms of the macro andmicro-geometry—which influence the amount and type of noise generated bythe teeth—may be tolerable within strict limits depending on the qualityrequirements, a “zero tolerance” policy applies to the edge zone of thetooth flank. Damage to the edge zone as a result of influence on thestructure will contribute to faster wear of the teeth and can, inextreme cases, cause the tooth to fracture and break off. In the contextof these requirements, different techniques may be useful all of whichare included within the scope of the present invention.

Exemplary gear grinding techniques include:

-   -   Gear grinding with the continuous generative grinding technique        using grinding worms: The bonded abrasive article (typically a        grinding wheel) has a shape that corresponds to a grinding worm,        the basic tooth profile of which should always be seen as a rack        profile. The involute form is generated through continuous        generative grinding of the grinding worm and the gearing). The        process lends itself very well to the series production of gear        wheels.    -   Gear grinding with globoidal grinding worms (continuous profile        grinding): unlike the continuous generative grinding technique,        the shape of the bonded abrasive article in this case does not        correspond to a grinding worm with a rack profile as the basic        tooth profile. Instead, a globoidal grinding worm maps the        contour of the tooth flank. During the grinding process the        tooth form is produced through virtually linear engagement of        the tool in the tooth gap. This method is predestined for        grinding bevel gears which are used primarily in differential        gears and can optionally be combined with a subsequent honing        step.    -   Single flank generating grinding: The involute shape is produced        in a generative grinding process in which the grinding wheel        only machines a single flank in the direction of grinding per        tooth gap. This method allows the machining of different moduli        with an unchanged wheel width and allows different infeeds for        the left or right-hand tooth flank.    -   Form or profile grinding with radial infeed: The involute form        is transferred to the bonded abrasive article (most typically a        grinding wheel), which then generates the form in the tooth gap        of the workpiece.    -   Form or profile grinding with rotative infeed: The involute form        is transferred to the bonded abrasive article (typically a        grinding wheel), which then generates the form in the tooth gap        of the workpiece.

Bonded abrasive articles for use in the gear grinding applications arenot particularly limited and as described in the foregoing. In preferredembodiments, the bonded abrasive articles for use in gear grindingapplications may be characterized by a particle shape selected from flattriangles or flat rectangles wherein optionally at least one face isshaped inwardly, as described in the foregoing with respect toparticularly preferred particle shapes.

Creep-Feed Grinding

Creep-feed grinding can be considered as a specific case of surfacegrinding. However, in contrast to surface grinding with a reciprocatinglinear cutting motion, creep-feed grinding uses relatively large cuttingdepths but comparatively low feed rates. The total grinding allowance isgenerally achieved in a few passes. With creep-feed grinding, adistinction is made between surface grinding and cylindrical grindingoperations. One special form of creep-feed grinding is outside-diameterlongitudinal grinding (peel grinding).

Creep-feed grinding typically uses rotating dressing devices and istypically operated wet. With creep-feed grinding, the workpiece form canbe produced with large infeeds of up to 15 mm in a single grinding pass.As with increasing infeed the length of contact between the workpieceand the bonded abrasive article increases significantly, the processesof transporting the grinding fluid and carrying away the grindingdetritus is made more difficult. As a result, creep-feed grindingrequires open-pored abrasive articles with a low hardness and acontinuous supply of grinding fluid in large quantities. This method isparticularly well suited to the final cutting of high-precision profileslike guideways and clamping profiles of turbine vanes.

Bonded abrasive articles for use in creep-feed grinding applications arenot particularly limited and as described in the foregoing. In preferredembodiments, the bonded abrasive articles for use in creep-feed grindingapplications may be characterized by a particle shape selected from flattriangles or flat rectangles wherein optionally at least one face isshaped inwardly, as described in the foregoing with respect toparticularly preferred particle shapes.

Surface Grinding (Except Creep-Feed Grinding)

Surface grinding or face grinding techniques are commonly divided intoperipheral-longitudinal surface grinding (surface grinding, facegrinding of large surfaces) and peripheral-transverse surface grinding(flute grinding, profile grinding).

In the case of peripheral-longitudinal grinding, the grinding wheelengages at right angles and advances by the selected feed increment intothe workpiece, which is moved by the machine table. In the process, theinfeed and feed rate define the grinding result.

Peripheral-transverse surface grinding is ideally suited to producinglarge, flat surfaces. With this method, the bonded abrasive article isalso positioned at right angles to the workpiece, but it is fed in bythe amount which exactly corresponds to the width of the bonded abrasivearticle. Both methods can be used for reciprocating grinding andcreep-feed grinding.

With reciprocating grinding, the bonded abrasive article moves over theworkpiece “backwards and forwards” at right angles to the referenceedge—the resulting motion is described as being “reciprocating”. Thismethod is seen as the oldest variant of surface grinding and ischaracterised by low cutting depths (for example as low as 0.005 to 0.2mm) and high table speeds (for example ranging from 15 to 30 m/min). Thetechnique is particularly useful for materials which are easy to grind,small batch sizes and low amounts of material removal, as well in casesof relatively low machine investment.

Bonded abrasive articles for use in surface grinding applications arenot particularly limited and as described in the foregoing. In preferredembodiments, the bonded abrasive articles for use in surface grindingapplications may be characterized by a particle shape selected from flattriangles or flat rectangles wherein optionally at least one face isshaped inwardly, as described in the foregoing with respect toparticularly preferred particle shapes

Cylindrical Grinding

Cylindrical grinding is a grinding technique which is commonlycharacterized by having one or more and preferably all of the followingfour features:

(1) The workpiece is constantly rotating; (2) The grinding wheel isconstantly rotating; (3) The grinding wheel is fed towards and away fromthe work; (4) Either the work or the grinding wheel is traversed withthe respect to the other.

While the majority of cylindrical grinding applications employ all fourmovements, there are applications that only employ three of the fouractions. Three main types of cylindrical grinding are outside diameter(OD) grinding, inside diameter (ID) grinding, and centerless grindingand any one of these techniques can be suitably used in the presentinvention:

-   -   Outside diameter (OD) grinding is one of the most frequently        used grinding techniques—for example in the automotive industry,        where it is used in the grinding of camshafts and crankshafts.        During the course of industrial development and in response to        the requirements which have emerged as a result, outside        diameter grinding has been divided into different variants of        the technique which differ depending on the way in which the        workpiece is mounted and according to the principle feed        direction.        -   Peripheral-transverse outer diameter (OD) grinding between            centers (also known as plunge grinding)        -   Centerless peripheral-transverse outer diameter (OD)            grinding        -   Peripheral-longitudinal outer diameter (OD) grinding between            centers (also known as throughfeed grinding)        -   Centerless peripheral-longitudinal outer diameter (OD)            grinding

In processes of grinding between centers, the workpiece is clampedfirmly between two centers in centering fixtures on its end faces, andin this position the workpiece is driven by the grinding machine.Depending on the principle feed direction of the wheel—right-angledplunge feed or parallel movement along the workpiece—this is referred toas transverse or longitudinal grinding.

-   -   In the process of peripheral-transverse outer diameter grinding,        the grinding wheel is generally at right angles to the        workpiece. This technique is generally used to machine bearing        seats, shoulders and grooves using straight plunge grinding.        Often the cut-in is divided into several process steps which are        performed in sequence with ever decreasing chip removal rates.        Depending on the particular task and the size of the batch,        angle plunge grinding is another variant which may be more        productive.    -   The process of peripheral-longitudinal outer diameter grinding        is particularly suitable for applications requiring cylindrical        or conical workpieces which are significantly longer than the        width of the grinding wheel. Examples include but are not        limited to the machining of press cylinders and rollers for        paper production, as well as rollers for use in rolling mills in        the steel industry. In this technique the grinding wheel moves        parallel to the workpiece and is fed in at the reversal point at        right angles to the workpiece. The required finished dimension        can either be attained in several passes or in just a single        pass—the latter being referred to as peel grinding. These        methods are comparable to creep-feed grinding and reciprocating        grinding. In the automotive industry, peel grinding is used for        example in the production of drive shafts.    -   Centerless grinding: If the challenge is to machine large        quantities of long and/or thin, round components made of pliable        or brittle materials, centerless grinding might be the solution.        In addition, centerless grinding is a technique which can allow        multiple tasks—e.g. roughing and finishing—to be performed in a        single pass. The machining process itself corresponds to the        other cylindrical grinding techniques like the ones previously        mentioned with respect to “Outside diameter grinding”—even        without centers the process still involves plunge grinding and        through feeding techniques.    -   Internal diameter (ID) grinding provides perfect functional        surfaces in components which need to establish a non-positive        connection with an axle or shaft. Similarly to outer diameter        (OD) grinding, this method is split into two different        techniques according to the direction of grinding:        -   Peripheral-transverse internal diameter (ID) grinding            (plunge grinding)        -   Peripheral-longitudinal internal diameter (ID) grinding    -   In terms of the behaviour of the grinding wheel and the        workpiece, both techniques display virtually identical        properties to outer diameter (OD) grinding between centres.        Application examples where ID grinding is commonly used include        but are not limited to the refining of bores with a        high-precision fit; for the machining of hard and super-hard        materials, to machine different diameters in a single pass as        well as to produce tapered fits and in situations where the        grinding wheel needs to be narrower than the surface which is to        be machined and a combination of longitudinal and plunge        grinding is required. In typical cases the grinding wheel        diameter should not exceed ⅔ or a maximum of ⅘ of the bore        diameter.

Bonded abrasive articles for use in cylindrical grinding applicationsare not particularly limited and as described in the foregoing. Inpreferred embodiments, the bonded abrasive articles for use incylindrical grinding applications may be characterized by a particleshape selected from flat triangles or flat rectangles wherein optionallyat least one face is shaped inwardly, as described in the foregoing withrespect to particularly preferred particle shapes.

Surprisingly, bonded abrasive articles in accordance with the presentinvention have been found to provide excellent results in a wide rangeof grinding applications and in particular in high performance grindingapplications.

For the purposes of the present invention, the term high performancegrinding application is intended to refer to higher material removalrates than is commonly possible with present day conventional abrasives.Conventional abrasives encompass all types of aluminium oxide includingso-called ceramic abrasives, and silicon carbide.

High performance grinding can be established for a specific grindingapplication based on the knowledge of sound grinding engineering andadequate modern CNC (Computerized Numerical Control) machinery. Oneparameter to define high performance grinding could be the specificmaterial removal rate Q′_(W) also called Q-prime. Q′_(W) indicates howmany mm³ of workpiece material one mm wheel width removes per second(mm³/mm/sec). Q′_(w) can be calculated based on two parameters, namelythe depth of cut a_(e) and the feed rate v_(w), according to the formulaQ′_(W)=[a_(e)×v_(w)]/60. The specific material removal rate Q′_(w) canbe increased by increasing the feed rate v_(W) and/or the depth of cuta_(e). [The peripheral speed v_(c) does not have an influence onQ′_(w)]. Values for Q′_(w) are typically indicated by using the unitmm³/mm/s or mm³/(mm·s).

Typical ranges for Q′_(W) for exemplary high performance grindingapplications can be specified as follows: Inner diameter (ID-) grinding1-15, preferably 2-12, most preferably 4-11 mm³/mm/s; outer diameter(OD-) grinding 1.5-25, preferably 3-22, most preferably 4-20 mm³/mm/s;surface grinding 1.5-20, preferably 2-17, most preferably 4-19 mm³/mm/s;profile grinding 3-60, for example 3-50, preferably 5-45, mostpreferably 7-50 or 7-40 mm³/mm/s; profile grinding with generatingmethod 8-60, preferably 10-55, most preferably 14-50 mm³/mm/s;creep-feed grinding 4-100, preferably 6-90, most preferably 9-80mm³/mm/s; and camshaft grinding 8-100, preferably 12-95, most preferably1.5-90 mm³/mm/s.

While the values mentioned above refer to roughing and semi-roughingoperations, in finishing operations the Q′_(W) values may be <1mm³/mm/s.

Bonded abrasive articles of the present invention have been found toprovide constant grinding results over a long period of time andparticularly under severe grinding conditions (for example at highspecific material removal rates).

In addition, bonded abrasive articles in accordance with the presentinvention can provide a better surface finish (decreased surfaceroughness R_(a)) on the workpiece used in a wide range of grindingapplications ranging from roughing via semi-roughing to finishingoperations. In some instances, bonded abrasive articles incorporating acoarser particle size of shaped abrasive particles may surprisinglyprovide better surface quality as compared to a finer particle size.

During use the bonded abrasive articles can also ensure a reduced riskof damaging the workpiece (such as by workpiece burning ordiscoloration) while at the same time minimizing the clogging of thebonded abrasive article during use.

Bonded abrasive articles of the present invention are characterized bylong dressing cycles thus allowing more workpiece parts to be finalizedbetween dressing cycles as well as a long total serve life of the bondedabrasive article.

Due to the high material removal rates which can be realized usingbonded abrasive articles of the present invention, shorter grindingtimes can be accomplished contributing to a higher workpiece flow inoverall.

Another parameter which is often used to characterize the performance ofa grinding application is the specific chip volume V′_(w). V′_(w)indicates the total amount of workpiece material [mm³] that is removedin a grinding application before dressing has to be set up (i.e. duringone grinding cycle). The time after which dressing has to be set up(i.e., the end of the grinding cycle) can be easily recognized by aperson skilled in the art of grinding. By way of example, the end of agrinding cycle is typically indicated by a somewhat prominent drop inthe power drawn by the grinding machine. Other factors which can be usedas additional or alternative indicators for recognizing the end of agrinding cycle include but are not limited to the loss of the form andprofile holding of the bonded abrasive article, decrease of workpiecequality, for example burning or discoloration of the workpiece, or worsesurface finish indicated by an increased surface roughness Ra.

At the end of a grinding cycle, the specific chip volume can be easilycalculated by a skilled person, as is known in the art. For the purposeof determining the specific chip volume, the actual start of grinding istaken as the starting point of the grinding cycle. For evaluating theperformance of a specific grinding application, the specific materialremoval rate Q′_(w) is typically set constant and the performance of thegrinding application is evaluated with respect to the specific chipvolume V′_(w).

In practice, the specific chip volume is commonly based on the effectivewidth of the active abrasive article's profile used in the grindingapplication (i.e. the specific chip volume indicates the total volume ofworkpiece material removed per 1 mm of width of the bonded abrasivearticle, for example 1 mm wheel width during one grinding cycle).

Bonded abrasive articles in accordance with the present invention havesurprisingly been found to provide excellent results with respect to thespecific chip volume V′_(w), in particular in applications such as geargrinding, thus for example leading into higher set limits forredressing. It is to be emphasized that such excellent results withrespect to the chip volume surprisingly can also be achieved at highmaterial removal rates i.e., when using a high constant value of Q′_(w)during the grinding cycle, for example when using gear grinding (such assingle rib ear grinding) with a specific material removal rate Q′_(w) ofat least 5 mm³/mm/s, typically of at least 10 mm³/mm/s, more typicallyof at least 14 mm³/mm/s or at least 16 mm³/mm/s and even more typicallyof at least 20 mm³/mm/s, preferably of at least 25 mm³/mm/s and morepreferably of at least 30 mm³/mm/s. Typically, abrasive articles basedon conventional abrasive particles show lower specific chip volumes at ahigher specific material removal rate Q′_(w) as compared to the samegrinding application at a lower specific material removal rate Q′_(w)and typically show adverse effects with respect to the workpiece such asburning or discoloration when used at higher specific material removalrates. Even under these severe grinding conditions no workpiece burningor discoloration was observed when using bonded abrasive articles inaccordance with the present invention.

While in particular grinding applications such as gear grindingapplications have been found to provide such excellent results withrespect to the specific chip volume, other grinding applications areexpected to provide similar pronounced effects.

Bonded abrasive articles in accordance with the present inventionincorporating shaped abrasive particles as defined herein can providespecific chip volumes that are substantially higher than those commonlyachieved with present day conventional abrasives (as defined withrespect to high performance grinding applications). In other words,using a given set of grinding conditions [given workpiece, givengrinding application at constant Q′_(w); for example 17CrNiMo6, geargrinding at a constant specific material removal rate Q′_(W) of 14mm³/mm/s (or even with a specific material removal rate Q′_(W) as highas 30 mm³/mm/s)], a bonded abrasive article in accordance with thepresent invention typically provides a specific chip volume that is atleast 20% higher, more typically at least 50%, higher, even moretypically at least 100% higher, even more typically at least 200% higherand most typically at least 300% higher than the specific chip volumeachieved when using a comparable bonded abrasive article using the sameset of grinding conditions (in particular the same specific materialremoval rate Q′_(W)).

A person skilled in the art of grinding can easily ascertain anappropriate comparable bonded abrasive article. A bonded abrasivearticle suitable for use as a comparable bonded abrasive article can forexample be based on the same abrasive material but with the onlydifference that the abrasive particles are not shaped. For example, thesame bonded abrasive article but wherein the shaped abrasive particlesaccording to the invention are replaced with the same nominal size andweight of crushed abrasive particles having the same chemicalcomposition could be used as a comparable bonded abrasive article. Acomparable bonded abrasive article should also contain the same nominalsize(s) and weight(s) of any optional secondary abrasive particleshaving the same chemical composition(s) as used in the bonded abrasivearticle to be evaluated. Hence, the shaped abrasive particles as definedherein contained in the bonded abrasive article to be evaluatedpreferably represent the only difference to the comparable bondedabrasive article used when evaluating the specific chip volume V′_(w).That means that the same type (particularly with respect to the chemicalcomposition) and volume amount of bonding medium (and optionally thesame volume amount of porosity, if any) is preferably used for thebonded abrasive article to be evaluated and the comparable bondedabrasive article.

By way of illustration, specific chip volumes as achievable in thepresent invention are typically higher by factor 2, or 5, or 10, or 15and even 20 than what is commonly achieved with a comparable bondedabrasive article based on such present day conventional abrasives.

For example, using a bonded abrasive article of the present invention, agrinding application [such as gear grinding (particularly single ribgear grinding) a workpiece made of for example 17CrNiMo6 with a specificmaterial removal rate Q′_(w) of for example 14 mm³/mm/s] can easilyprovide specific chip volumes of at least 850 mm³/mm, particularly of atleast 1500 mm³/mm greater, more particularly of at least 2500 mm³/mm,even more particularly of at least 10000 mm³/mm and even moreparticularly of 15 000 mm³/mm or greater or of even 30 000 mm³/mm orgreater.

The present invention thus also relates to a method of grinding (inparticular, a method of gear grinding, more particularly single rib geargrinding) characterized by using a bonded abrasive article according tothe present invention, wherein the specific chip volume V′_(w) is atleast 20% higher, preferably at least 50% higher, more typically atleast 100% higher, even more typically at least 200% higher and mosttypically at least 300% higher than the specific chip volume achievedwhen using a comparable bonded abrasive article under the same set ofgrinding conditions, in particular at the same specific material removalrate Q′_(w).

The present invention also relates to a method of grinding (inparticular, a method of single rib gear grinding at a specific materialremoval rate of Q′_(w) of 14) characterized by using a bonded abrasivearticle according to the present invention, wherein the specific chipvolume is at least 850 mm³/mm, particularly at least 1 500 mm³/mmgreater, preferably at least 2 500 mm³/mm, more preferably at least 10000 mm³/mm and even more preferably 15 000 mm³/mm or greater or at least30 000 mm³/mm or greater. In other preferred embodiments, the presentinvention relates to a method of grinding (in particular, a method ofsingle rib gear grinding at a specific material removal rate of Q′_(w)of 16) characterized by using a bonded abrasive article according to thepresent invention, wherein the specific chip volume is at least 850mm³/mm, particularly at least 1 500 mm³/mm greater, preferably at least2500 mm³/mm, more preferably at least 10 000 mm³/mm and even morepreferably 15 000 mm³/mm or greater or at least 30 000 mm³/mm orgreater, and in other preferred embodiments is more than 10 000 mm³/mm,preferably at least 11 000, even more preferably 15 000 mm³/mm orgreater and most preferably 30 000 mm³/mm or greater.

Other effects achieved in the present invention are high form or profileholding of the bonded abrasive article. This translates into lessdressing, and therefore better process and tool consumption economics.

The use of shaped abrasive particles (such as flat triangles and flatrectangles as described herein, optionally having one or more facesshaped inwardly), in vitrified bonded abrasive articles allows thesebeneficial effects to be achieved for a wide range of differentcompositions of the bonded abrasive article as well as for a widevariety of applications. Although in some applications a most pronouncedeffect might be achieved when the abrasive article comprises 100% shapedabrasive particles in accordance with the present invention based on thetotal amount of abrasive particles present in the article, articlescontaining for example as little as 5% by weight of shaped abrasiveparticles in accordance with the present invention and up to 95% byweight of secondary abrasive particles, based on the total amount ofabrasive particles present in the article, have also been shown toprovide excellent performance over a wide range of applications.

The effects achieved in the present invention are also unexpected inview of the fact that the bonded abrasive article typically does nothave to comprise the shaped abrasive in any specific orientation. Unlikethe situation in comparatively thin coated abrasive articles whereorientation may be of advantage, the bonded abrasive article (forexample, wheel, segment, layer or part thereof) typically comprises theshaped abrasive particles in a random orientation, although orientationof the particles is not excluded from the scope of the presentinvention.

In embodiments, the present invention relates to the following items:

-   1. A bonded abrasive article comprising shaped abrasive particles    and a bonding medium comprising a vitreous bond, said shaped    abrasive particles each comprising a first side and a second side    separated by a thickness t, wherein said first side comprises a    first face having a perimeter of a first geometric shape.-   2. The article of item 1, wherein the thickness t is equal to or    smaller than the length of the shortest side-related dimension of    the particle.-   3. The article according to items 1 or 2, wherein the shaped    abrasive particles are ceramic shaped abrasive particles.-   4. The article according to any of items 1 to 3, wherein the shaped    abrasive particles comprise alpha alumina.-   5. The article according to any of items l to 4, wherein the shaped    abrasive particles comprise non-seeded sol-gel derived alpha    alumina.-   6. The article according to any of items 1 to 4, wherein the shaped    abrasive particles comprise seeded sol-gel derived alpha alumina.-   7. The article according to any of items 1 to 6, further comprising    secondary abrasive particles.-   8. The article according to item 7, wherein the shaped and secondary    abrasive particles are independently selected from particles of    fused aluminum oxide materials, heat treated aluminum oxide    materials, ceramic aluminum oxide materials, sintered aluminum oxide    materials, silicon carbide materials, titanium diboride, boron    carbide, tungsten carbide, titanium carbide, diamond, cubic boron    nitride, garnet, fused alumina-zirconia, sol-gel derived abrasive    particles, cerium oxide, zirconium oxide, titanium oxide or a    combination thereof.-   9. The article according to item 7 or 8, wherein the secondary    abrasive particles are selected from crushed abrasive particles    having a specified nominal grade.-   10. The article according to item 9, wherein the crushed abrasive    particles are of a smaller size than the shaped abrasive particles.-   11. The article according to any of items 1 to 10 comprising 10 to    80% by volume of said shaped abrasive particles.-   12. The article according to any of items 1 to 11 comprising 1 to    60% by volume of said bonding medium.-   13. The article according to any of items 1 to 12, wherein said    vitreous bond comprises, based on the total weight of the vitreous    bond, 25 to 90% by weight of SiO₂; 0 to 40% by weight of B₂O₃; 0 to    40% by weight of Al₂O₃; 0 to 5% by weight of Fe₂O₃, 0 to 5% by    weight of TiO₂, 0 to 20% by weight of CaO; 0 to 20% by weight of    MgO; 0 to 20% by weight of K₂O; 0 to 25% by weight of Na₂O; 0 to 20%    by weight of Li₂O; 0 to 10% by weight of ZnO; 0 to 10% by weight of    BaO; and 0 to 5% by weight of metallic oxides.-   14. The article according to any of items 1 to 13, wherein the    vitreous bond is obtainable from a vitreous bond precursor    composition comprising fit.-   15. The article according to any of item 14, wherein the vitreous    bond precursor composition comprises 3 to 70% by weight of a fit    based on the total weight of the vitreous bond precursor    composition.-   16. The article according to any of items 1 to 15, comprising    porosity.-   17. The article according to any of items 1 to 1.6 comprising, based    on the volume of the article, 1 to 60% by volume of a vitreous bond,    10 to 80% by volume of shaped abrasive particles and 5 to 80% by    volume of porosity.-   18. The article according to any of items 7 to 17 wherein the shaped    abrasive particles and the secondary abrasive particles are    comprised in a blend, wherein the content of the secondary abrasive    particles is up to 95% by weight based on the total weight of    abrasive particles present in the blend.-   19. The article according to any of items 1 to 18, wherein the ratio    of the length of the shortest side-related dimension to the    thickness of said particle is at least 1:1.-   20. The article according to any of items 1 to 19, wherein said    first geometric shape is selected from polygonal shapes,    lense-shapes, lune-shapes, circular shapes, semicircular shapes,    oval shapes, circular sectors, circular segments, drop-shapes and    hypocycloids.-   21. The article according to any of items 1 to 20 wherein said first    geometric shape is selected from triangular shapes and quadrilateral    shapes.-   22. The article according to any of items 1 to 21 wherein said first    geometric shape is a quadrilateral shape selected from a rectangle,    a rhombus, a rhomboid, a kite, or a superellipse.-   23. The article according to any of items 1 to 21 wherein said first    geometric shape is a triangular shape selected from isosceles    triangular shapes and equilateral triangular shapes.-   24. The article according to any of items 1 to 23, wherein the    shaped abrasive particles have a volumetric aspect ratio and the    volumetric aspect ratio is greater than about 1.15.-   25. The article according to any of items 1 to 24, comprising at    least one sidewall.-   26. The article according to item 25, wherein the sidewall comprises    one or more facets.-   27. The article according to item 26, wherein the one or more facets    have a shape independently selected from triangular and    quadrilateral geometric shapes and combinations thereof.-   28. The article according to any of items 25 to 27, wherein the at    least one sidewall is a sloping sidewall.-   29. The article according to any of items 25 to 28, further    comprising a draft angle alpha between the second face and the    sidewall, the draft angle alpha being greater than 90 degrees.-   30. The article of item 29, wherein the draft angle alpha is between    about 95 to about 135 degrees.-   31. The article according to any of items 25 to 28, wherein the    sidewall intersects the first side at an angle beta of between 5 to    about 65 degrees.-   32. The article according to any of items 1 to 31, wherein said    shaped abrasive particles each comprise at least one shape feature    selected from: an opening, at least one recessed (or concave) face;    at least one face which is shaped outwardly (or convex); at least    one side having a plurality of grooves or ridges; at least one    fractured surface; a low roundness factor; a perimeter of the first    face comprising one or more corner points having a sharp tip; a    second side comprising a second face having a perimeter comprising    one or more corner points having a sharp tip; or a combination of    one or more of said shape features.-   33. The article according to any of items 1 to 32, wherein the    shaped abrasive particles each have an opening.-   34. The article according to any of item 33, wherein the opening    passes through the first side and the second side.-   35. The article according to any of items 1 to 34, wherein the    shaped abrasive particles further comprise a plurality of grooves    and/or ridges on the second side.-   36. The article according to any of items 1 to 35 wherein the second    side comprises a vertex or a ridge line or a second face.-   37. The article according to item 36, wherein the second side    comprises a second face separated from the first side by thickness t    and at least one sidewall connecting the second face and the first    face.-   38. The article according to item 37, wherein the thickness is equal    to or smaller than the length of the shortest facial dimension of    the particle.-   39. The article according to item 37 or 38, wherein the second face    has a perimeter of a second geometric shape which may be the same or    different to the first geometric shape.-   40. The article according to item 39, wherein said first and second    geometric shapes are independently selected from regular polygons,    irregular polygons, lenses, lunes, circulars, semicirculars, ovals,    circular sectors, circular segments, drop-shapes and hypocycloids.-   41. The article according to items 39 or 40, wherein the first and    second geometric shapes have identical geometric shapes which may or    may not be different in size.-   42. The article according to item 41, wherein the first and second    geometric shapes are selected from substantially triangular shapes.-   43. The article according to item 42, wherein the substantially    triangular shape comprise the shape of an equilateral triangle.-   44. The article according to any of items 37 to 43, wherein the    first face and the second face are substantially parallel to each    other.-   45. The article according to any of items 37 to 44, wherein the    first face and the second face are nonparallel to each other.-   46. The article according to any of items 37 to 45, wherein the    sidewall is a sloping sidewall.-   47. The article according to any of items 37 to 46, further    comprising a draft angle alpha between the second face and the    sidewall, and the draft angle alpha is greater than 90 degrees.-   48. The article according to item any of items 37 to 47 comprising a    first sloping sidewall having a first draft angle, a second sloping    sidewall having a second draft angle, and a third sloping sidewall    having a third draft angle.-   49. The article according to item 48, wherein the first draft angle,    and the second draft angle, and the third draft angle have different    values from each other.-   50. The article according to item 48, wherein the first draft angle,    the second draft angle, and the third draft angle are equal.-   51. The article according to any of items 37 to 50, wherein the    first and the second face are substantially planar.-   52. The article according to any of items 37 to 50, wherein at least    one of the first and second face is a non-planar face.-   53. The article according to item 52, wherein the first face is    recessed or concave and the second face is substantially planar.-   54. The articles according to item 52, wherein the first face is    convex and the second face is recessed or concave.-   55. The article according to item 52, wherein the first face is    recessed or concave and the second face is recessed or concave.-   56. The article according to item 52, wherein the particles are    dish-shaped abrasive particles each having a sidewall and a varying    thickness t, wherein the first face is recessed and a thickness    ratio of Tc/Ti for the dish-shaped abrasive particles is between    1.25 to 5.00.-   57. The article according to item 52 or 56, wherein the first face    comprises a substantially planar center portion and a plurality of    raised corners.-   58. The article according to any of items 37 to 57, wherein the    second side comprises a second face and four facets intersecting the    second face at a draft angle alpha forming a truncated pyramid.-   59. The article of item 58, wherein the draft angle alpha is between    about 95 to about 135 degrees.-   60. The article according to item 36, wherein the second side    comprises a vertex separated from the first side by thickness t and    at least one sidewall connecting the vertex and the perimeter of the    first face.-   61. The article according to item 60, wherein the sidewall comprises    one or more facets connecting the vertex and the perimeter of the    first face.-   62. The article according to item 60 or 61, wherein the perimeter of    the first face is trilateral, quadrilateral or higher polygonal and    wherein the second side comprises a vertex and the corresponding    number of facets for forming a pyramid.-   63. The article according to any of items 60 to 62, wherein the    first side comprises a quadrilateral having four edges and four    vertices with the quadrilateral being selected from the group    consisting of a rectangle, rhombus, a rhomboid, a kite, or a    superellipse.-   64. The article according to any of items 60 to 62, wherein the    first side comprises a trilateral having three edges and three    vertices and the second side comprise a vertex and three triangular    facets forming a pyramid.-   65. The article according to item 64, wherein the trilateral is an    equilateral triangle.-   66. The article according to any of items item 60 to 65, wherein the    sidewall and/or or facets intersect the first side at an angle beta    of between about 5 to about 65 degrees.-   67. The article according to item 64, wherein the shaped abrasive    particles have four major sides joined by six common edges, wherein    each one of the four major sides contacts three other of the four    major sides, and wherein the six common edges have substantially the    same length.-   68. The article according to item 67, wherein at least one of the    four major sides is substantially planar.-   69. The article according to item 67 or 68, wherein at least one of    the four major sides is concave.-   70. The article according to item 67, wherein all of the four major    sides are concave.-   71. The article according to item 67 or 68, wherein at least one of    the four major sides is convex.-   72. The article according to any of items 67 to 71, wherein the    shaped abrasive particles have tetrahedral symmetry.-   73. The article according to any of items 67 to 72, wherein the    shaped particles are substantially shaped as regular tetrahedrons.-   74. The article according to item 36, wherein the second side    comprises a ridge line separated from the first side by thickness t    and at least one sidewall connecting the ridge line and the    perimeter of the first face.-   75. The article according to item 74, wherein the sidewall comprises    one or more facets connecting the ridge line and the perimeter of    the first face.-   76. The article according to any of item 74 or 75 wherein the    sidewall and/or facets intersect the first side at an angle beta of    between about 5 to about 65 degrees.-   77. The article according to any of items 74 to 76, wherein the    first geometric shape is selected from quadrilateral geometric    shapes and the sidewall comprises four facets forming a roof-shaped    particle.-   78. The article according to item. 77 wherein the quadrilateral    shape is selected from the group consisting of a rectangle, a    rhombus, a rhomboid, a kite, or a superellipse.-   79. The articles according to any of items 1 to 78, wherein the    abrasive particles have an average tip radius and the average tip    radius is less than 75 microns.-   80. The article according to any of items 1 to 79, wherein the    shaped abrasive particles each have a cross-sectional shape along a    longitudinal axis of the shaped abrasive particles, the    cross-sectional shape comprising a non-circular cross-sectional    plane, and the shaped abrasive particles comprise an Average    Roundness Factor of between about 15% to 0%.-   81. The article according to any of items 1 to 80 having a    three-dimensional shape selected from the shape of a wheel, honing    stone, grinding segment, mounted points or other shapes.-   82. The article according to any of items 1 to 81, wherein the    article comprises a wheel.-   83. The article according to any of items 1 to 82, wherein the    article is a wheel.-   84. The article according to any of items 82 or 83, wherein the    wheel is selected from grinding wheels for cylindrical grinding,    centerless grinding, surface and profile grinding, reciprocating    grinding, creep-feed grinding, grinding in generating methods of    gears, threads, tools, camshafts, crankshafts bearings, and guard    rails.-   85. The article according to any of items 1 to 84, wherein the    shaped abrasive particles are homogeneously distributed in the    abrasive article.-   86. The article according to any of items 1 to 84, wherein the    shaped abrasive particles are non-homogeneously distributed in the    abrasive article.-   87. The article according to item 86, which is or comprises a bonded    abrasive wheel, the wheel comprising an outer zone and an inner    zone, wherein the compositions of the inner and outer zone differ in    one or more aspects selected from the composition of the bond, the    shape of abrasive particles, the grit size of abrasive particle, and    the amount of abrasive particles.-   88. Use of an article according to any of items 1 to 87 in high    performance grinding applications.-   89. Use according to claim 88 for outer diameter grinding with a    Q′_(w) of at least 1.5 mm³/mm/sec, inner diameter grinding with a    Q′, of at least 1 mm³/mm/sec, surface grinding with a Q′_(w) of at    least 1.5 mm³/mm/sec, profile grinding with a Q′_(w) of at least 3    mm³/mm/sec, profile grinding with generating method with a Q′_(w) of    at least 8 mm³/mm/sec, creep-feed grinding with a Q′_(w) of at least    4 mm³/mm/sec, and camshaft grinding with a Q′_(w) of at least 8    mm³/mm/sec.-   90. Use of an article according to any of claims 1 to 87 for    abrading a workpiece material selected from steels, non-ferrous    metals, alloys, hard metals, ceramics and glasses.-   91. Method for abrading a workpiece, the method comprising    frictionally contacting at least a portion of the abrasive article    according to any of items 1 to 87 with a surface of a workpiece; and    moving at least one of the workpiece or the abrasive article to    abrade at least a portion of the surface of the workpiece.-   92. A method of grinding characterized by using a bonded abrasive    article according to any of items 1 to 87, wherein the specific chip    volume V′_(w) is at least 20% higher, than the specific chip volume    achieved when using a comparable bonded abrasive article at the same    specific material removal rate Q′_(w).

In particularly preferred embodiments, the present invention relates tothe following items:

-   1. A bonded abrasive article comprising shaped abrasive particles    and a bonding medium comprising a vitreous bond, said shaped    abrasive particles each comprising a first side and a second side    separated by a thickness t, wherein said first side comprises (or    preferably is) a first face having a perimeter of a first geometric    shape, wherein the thickness t is equal to or smaller than the    length of the shortest side-related dimension of the particle,    wherein said second side comprises (or preferably is) a second face    having a perimeter of a second geometric shape, said second side    being separated from said first side by thickness t and at least one    sidewall connecting said second face and said first face, said first    geometric shape and said second geometric shapes having    substantially identical geometric shapes which may or may not be    different in size, wherein said identical geometric shapes are both    selected either from triangular shapes or from quadrilateral shapes.-   2. The article according to item 1, wherein said identical geometric    shapes are both selected from triangular shapes.-   3. The article according to any of items 1 or 2, wherein the first    face and the second face are substantially parallel or non-parallel    to each other.-   4. The article according to any of items 1 to 3, wherein the first    and/or the second face are substantially planar.-   5. The article according to any of items 1 to 4, wherein at least    one of the first and second face is a non-planar face.-   6. The article according to item 5, wherein at least one of the    first and the second face is shaped inwardly.-   7. The article according to item 6, wherein the first face is shaped    inwardly and the second face is substantially planar or the first    face is shaped outwardly and the second face is shaped inwardly or    the first face is shaped inwardly and the second face is shaped    inwardly.-   8. The article according to any of items 1 to 7, wherein the second    side comprises a second face and four facets intersecting the second    face at a draft angle alpha forming a truncated pyramid.-   9. The article according to any of items 1 to 8, wherein the shaped    abrasive particles are ceramic shaped abrasive particles.-   10. The article according to any of items 1 to 9, wherein the shaped    abrasive particles comprise alpha alumina.-   11. The article according to any of items 1 to 10, wherein the    shaped abrasive particles comprise seeded or non-seeded sol-gel    derived alpha alumina.-   12. The article according to any of items 1 to 7, wherein said    shaped abrasive particles comprise a major portion of aluminum    oxide.-   13. The article according to item 12, wherein said aluminum oxide is    fused aluminum oxide.-   14. The article according to any of items 1 to 13, further    comprising secondary abrasive particles.-   15. The article according to item 14, wherein the shaped and    secondary abrasive particles are independently selected from    particles of fused aluminum oxide materials, heat treated aluminum    oxide materials, ceramic aluminum oxide materials, sintered aluminum    oxide materials, silicon carbide materials, titanium diboride, boron    carbide, tungsten carbide, titanium carbide, diamond, cubic boron    nitride, garnet, fused alumina-zirconia, sol-gel derived abrasive    particles, cerium oxide, zirconium oxide, titanium oxide or a    combination thereof.-   16. The article according to item 14 or 15, wherein the secondary    abrasive particles are selected from crushed abrasive particles    having a specified nominal grade.-   17. The article according to item 16, wherein the crushed abrasive    particles are of a smaller size than the shaped abrasive particles.-   18. The article according to any of items 14 to 17 wherein said    secondary abrasive particles are selected from particles of fused    aluminum oxide materials, particles of superabrasive materials or    particles of silicon carbide materials.-   19. The article according to any of items 1 to 18 comprising 10 to    80% by volume of said shaped abrasive particles and 1 to 60% by    volume of said bonding medium.-   20. The article according to any of items 1 to 19, wherein said    vitreous bond comprises, based on the total weight of the vitreous    bond, 25 to 90% by weight of SiO₂; 0 to 40% by weight of B₂O₃; 0 to    40% by weight of Al₂O₃; 0 to 5% by weight of Fe₂O₃, 0 to 5% by    weight of TiO₂, 0 to 20% by weight of CaO; 0 to 20% by weight of    MgO; 0 to 20% by weight of K₂O; 0 to 25% by weight of Na₂O; 0 to 20%    by weight of Li₂O; 0 to 10% by weight of ZnO; 0 to 10% by weight of    BaO; and 0 to 5% by weight of metallic oxides.-   21. The article according to any of items 1 to 21, wherein the    vitreous bond is obtainable from a vitreous bond precursor    composition comprising frit.-   22. The article according to any of items 1 to 22, comprising    porosity.-   23. The article according to any of items 14 to 22 wherein the    shaped abrasive particles and the secondary abrasive particles are    comprised in a blend, wherein the content of the secondary abrasive    particles is up to 95% by weight based on the total amount of    abrasive particles present in the blend.-   24. The article according to item 1, wherein the at least one    sidewall is a sloping sidewall.-   25. The article according to any of items 1 to 24, wherein said    shaped abrasive particles each comprise at least one shape feature    selected from: an opening, at least one recessed (or concave) face;    at least one face which is shaped outwardly (or convex); at least    one side having a plurality of grooves or ridges; at least one    fractured surface; a low roundness factor; a perimeter of the first    face comprising one or more corner points having a sharp tip; a    second side comprising a second face having a perimeter comprising    one or more corner points having a sharp tip; or a combination of    one or more of said shape features.-   26. The article according to any of items 1 to 25, wherein the    shaped abrasive particles each have an opening.-   27. The article according to any of items 1 to 26, wherein the    shaped abrasive particles further comprise a plurality of grooves    and/or ridges on the second side.-   28. The article according to any of items 1 to 27 having a    three-dimensional shape selected from the shape of a wheel, honing    stone, grinding segment, mounted points, or other shapes.-   29. The article according to any of items 1 to 28, wherein the    article comprises a wheel.-   30. The article according to any of item 29, wherein the wheel is    selected from grinding wheels for cylindrical grinding, centerless    grinding, surface and profile grinding, reciprocating grinding,    creep-feed grinding, grinding in generating methods of gears,    threads, tools, camshafts, crankshafts bearings, and guard rails.-   31. The article according to any of items 1 to 30, wherein the    shaped abrasive particles are homogeneously distributed in the    abrasive article.-   32. The article according to any of items 1 to 31, wherein the    shaped abrasive particles are non-homogeneously distributed in the    abrasive article.-   33. The article according to item 32, which is or comprises a bonded    abrasive wheel, the wheel comprising an outer zone and an inner    zone, wherein the compositions of the inner and outer zone differ in    one or more aspects selected from the composition of the bond, the    shape of abrasive particles, the grit size of abrasive particle, and    the amount of abrasive particles.-   34. Use of an article according to any of items 1 to 32 in high    performance grinding applications.-   35. Use according to item 34 for outer diameter grinding with a    Q′_(w) of at least 1.5 mm³/mm/sec, inner diameter grinding with a    Q′_(w) of at least 1 mm³/mm/sec, surface grinding with a Q′_(w) of    at least 1.5 mm³/mm/sec, profile grinding with a Q′_(w) of at least    3 mm³/mm/sec, profile grinding with generating method with a Q′_(w)    of at least 8 mm³/mm/sec, creep-feed grinding with a Q′_(w) of at    least 4 mm³/mm/sec, and camshaft grinding with a Q′_(w) of at least    8 mm³/mm/sec.-   36. Use of an article according to any of items 1 to 32 for abrading    a workpiece material selected from steels, non-ferrous metals,    alloys, hard metals, ceramics and glasses.-   37. Method for abrading a workpiece, the method comprising    frictionally contacting at least a portion of the abrasive article    according to any of items 1 to 32 with a surface of a workpiece; and    moving at least one of the workpiece or the abrasive article to    abrade at least a portion of the surface of the workpiece.-   38. Method of gear grinding characterized by using a bonded abrasive    article according to any of items 1 to 32.-   39. Method of creep-feed grinding characterized by using a bonded    abrasive article according to any of items 1 to 32.-   40. Method of surface grinding characterized by using a bonded    abrasive article according to any of items 1 to 32.-   41. Method of cylindrical grinding characterized by using a bonded    abrasive article according to any of items 1 to 32.-   42. A method of grinding characterized by using a bonded abrasive    article according to any of items 1 to 32, wherein the specific chip    volume V′_(w) is at least 20% higher, than the specific chip volume    achieved when using a comparable bonded abrasive article at the same    specific material removal rate Q′_(w).

Determination of Particle Dimensions

The dimensions of the shaped abrasive particle (such as length, widthand thickness) can be determined using methods known in the art, forexample, by using conventional measuring tools such as rulers, verniercalipers, micrometers, or microscopy measurement techniques andtypically calculating the average of a suitable number of measurements.

For example, a measuring microscope such as a Nikon MM-40 obtained fromNikon Americas Inc. in Melville, N.Y. according to the following testmethod can be used: One or more shaped abrasive particles are supportedon a glass slide preferably by its largest substantially planar surface(if it has one) in contact with the glass slide (dished or concavesurface up if the particle has one.) The glass slide is then placed onthe Nikon MM-40 microscope stage. The stage has the ability to move inthe X and Y direction and it is also equipped with counters for the X-Ydistance travelled. The crosshair is aligned with one of the exteriorvertices of the shaped abrasive particle. For example, a thin triangularparticle would use one of the three vertices; a rectangular base pyramidwould use one of the four rectangular base vertices of the pyramid. TheX and Y counters are then reset to zero. The crosshair is then movedclockwise to the next exterior vertex of the geometry being measured andthe X and Y readings are recorded. The remaining exterior verticesmoving in a clockwise direction are then sequentially measured. The Xand Y coordinates of each exterior vertex can then be placed into aspreadsheet and the maximum dimension between any two of the verticescalculated using Pythagoras' theorem.

For a triangle the length is maximum distance between any two adjacentvertices of the three vertices. For a rectangle, the length is themaximum dimension between adjacent vertices. For an elongatedparallelogram, the length is the maximum dimension between adjacentvertices. For a kite or a rhombus, the length is the maximum dimensionbetween opposing vertices. The maximum dimension to determine length foralternative geometries can be determined by those of skill in the artwhen looking at the geometry in the microscope. The width can then bedetermined perpendicular to the length by using the coordinates ofselected vertices or by rotating the stage or slide such that the lengthdimension is parallel to the X-axis. For a triangle the width is themaximum distance between the side with the longest adjacent vertices andthe opposing vertex. For a rectangle, the width is the largest dimensionbetween the two pairs of shorter opposing vertices. For an elongatedparallelogram, the width is the maximum dimension between the side withthe longest adjacent vertices and the opposing side. For a kite or arhombus, the width is the shorter dimension between opposing vertices.The maximum dimension to determine width for alternative geometries canbe determined by those of skill in the art when looking at the geometryin the microscope.

The Nikon MM-40 microscope is also equipped with a Z-axis scale with acounter. To measure thickness, t, (height from glass slide) theviewfield is first focused on the upper surface of the glass slide usingthe 100× objective for maximum accuracy. The Z counter is then reset tozero. The viewfield is then moved to the highest possible point of theshaped abrasive particle that can be observed (a lower magnification maybe needed to find the highest point) and the microscope refocused atthat the highest point at the 100× magnification. The particle'sthickness is determined by the Z reading after refocusing.

At least 20 shaped abrasive particles are measured for the dimension ofinterest (individual length, individual width, individual thickness).The averages of the dimension of interest (individual lengths, widths,thickness dimensions) are determined to define the dimension (length,width, thickness) for the measured shaped abrasive particlesrespectively.

For the purposes of this measurement, the thickness of a particle havingan opening is measured at the site of the actual maximum thickness ofthe particle (i.e. typically not within the opening). The shortest siderelated dimension, the width and the length of a particle having anopening are typically measured without subtracting the length of overlapof the opening with any one of these dimensions (if any). For example,the width and length of an equitrilateral, prismatic particle having anopening extending between the first and the second side of uniformthickness t can be measured based on the perimeter of the first face (orthe second face) without taking into account the opening.

The volumetric aspect ratio can be determined using methods known in theart, for example by using the actual maximum and minimum cross sectionalareas of the particle, and/or exterior dimensions determined bymicroscopy measurement techniques as previously described andcalculating the average of a suitable number (for example 20 or more) ofindividual particle determinations. For an equilateral triangular shapedabrasive particle, the thickness and side length can be measured bymicroscopic techniques discussed above and the volumetric aspect ratiodetermined.

The radius of curvature can be measured by using image analysis forexample, using a CLEMEX VISION PE image analysis program available fromClemex Technologies, Inc. of Longueuil, Quebec, Canada, interfaced withan inverted light microscope, or other suitable image analysissoftware/equipment. Using a suitable polished cross-section takenbetween the first face and the second face may help in microscopicexamination of the edge or corner point of a sidewall. The radius ofcurvature of each point of the shaped abrasive article can be determinedby defining three points at the tip of each point (when viewed e.g. at100× magnification). A point is placed at the start of the tip's curvewhere there is a transition from the straight edge to the start of acurve, at the apex of the tip, and at the transition from the curved tipback to a straight edge. The image analysis software then draws an arcdefined by the three points (start, middle, and end of the curve) andcalculates a radius of curvature. The radius of curvature for at least30 apexes are measured and averaged to determine the average tip radius.

The Average Roundness Factor can be determined as described in [0029] to[0033] of US Patent Application Publication No. 2010/0319269 by using atransverse cut C, as defined in of said patent application publication.

Objectives and advantages of this disclosure are further illustrated bythe following non-limiting examples, but the particular materials andamounts thereof recited in these examples, as well as other conditionsand details, should not be construed to unduly limit this disclosure.

EXAMPLES

Unless otherwise noted, all parts, percentages, ratios, etc. in theExamples and the rest of the specification are by weight. Unlessotherwise noted, grinding was performed wet using lubricants common forthe grinding application, such as a 3 to 5% emulsion (v/v) of oil orsynthetic lubricant (for example Castrol Syntilo 81 E, available fromCastrol LTd. or Castrol Group, or Cimtech® D18, available from Cimcool®Fluid Technology, LLC) in water.

Materials Used in the Examples

80+ Shaped abrasive particles with the composition of 3M ™ CeramicAbrasive Grain 321 with each abrasive particle shaped as a triangularprism with sloping side walls (side wall draft angle 98 degrees) withtwo substantially parallel faces, wherein the first face comprises anequilateral triangle with a median dimension of 0.49 mm and the secondface also comprises an equilateral triangle of median edge length of0.415 mm. The average distance between the faces was 0.095 mm. 60+Shaped abrasive particles with the composition of 3M ™ Ceramic AbrasiveGrain 321 with each abrasive particle shaped as a triangular prism withsloping side walls (side wall draft angle 98 degrees) with twosubstantially parallel faces, wherein the first face comprises anequilateral triangle with a median dimension of 0.63 mm and the secondface also comprises an equilateral triangle of median edge length of0.540 mm. The average distance between the faces was 0.120 mm T Shapedabrasive particles with the composition of 3M ™ Ceramic Abrasive Grain321 with each abrasive particle shaped as a tetrahedron with a medianedge length of 0.510 mm White fused aluminium available as Alodur ® WSKfrom Treibacher Schleifmittel oxide AG, Austria in grit size F24, F30,F40, F46, F54, F60, F70, F80, and F100 according to FEPA-Standard 44-1:2006 Monocrystalline available as Alodur ® SCTSK from TreibacherSchleifmittel aluminium oxide AG, Austria in grit size F80 according toFEPA-Standard 44-1: 2006 3M ™ Ceramic Abrasive crushed non-seededsol-gel derived ceramic alpha alumina Grain 321 based abrasive particleshaving the same chemical composition: Al₂0₃ 94-96% MgO 1.2% +/− 0.3%Y₂0₃ 1.2% +/− 0.3% La₂0₃ + Nd₂0₃ 2.4% +/− 0.5% Traces of: Ti0₂, Si0₂,CaO, and CoO and Fe and having grit size ANSI 46, ANSI 60, ANSI 80 andANSI 90, available from 3M, USA Cerpass TGE ®, Code Extruded abrasiverods composed of seeded gel product; TGE-0557 containing ≧99.6% alphaaluminium oxide in grit size grit size 36 with an aspect ratio [theratio of the length to the greatest cross-sectional dimension (thegreatest dimension perpendicular to the length)] in the range of 2.9-4.5and a side dimension of the cross-sectional area of 474-546 μm, and ingrit size 100 with an aspect ratio [the ratio of the length to thegreatest cross-sectional dimension (the greatest dimension perpendicularto the length)] in the range of 3.3-5.1 and a side dimension of thecross-sectional area of 140-152 μm, Saint-Gobain Grains & Powders,Worcester, USA Cerpass XTL ®, Code Crushed seeded gel product,containing ≧99.6% alpha XTL-0560 aluminium oxide in grit size 90according to ANSI available from Saint-Gobain Grains & Powders Mix 1 -Comparative 100% by weight white fused aluminium oxide based on theExample Ref. 1A-2 total weight of abrasive grain, consisting of 20% byweight of FEPA grade F70, 50% by weight of FEPA grade F80, and 30% byweight of FEPA grade F100 Mix 2 - Comparative 30% by weight 3M ™ CeramicAbrasive Grain 321 and 70% Example Ref. 2A-1, by weight of white fusedaluminium oxide based on the total Comparative Example weight ofabrasive grain Ref. IX-3 The 3M ™ Ceramic Abrasive Grain 321 portionconsists of each 50% by weight of ANSI grade 80 and ANSI grade 90. Theportion of white fused aluminium oxide consists of each 28.6% by weightof FEPA grade F70 and F100, and 42.8% by weight of FEPA grade F80. Mix3 - Examples 1A-1, 30% by weight 80+ and 70% by weight white fusedalumina and 1B-1, Example V-4, by weight based on the total weight ofabrasive grain Example IX-1 The portion of white fused aluminium oxideconsists of each 28.6% by weight of FEPA grade F70 and F100, and 42.8%by weight of FEPA grade F80 Mix 4 - Examples 2A-1, 30% by weight 60+ and70% by weight of white fused and 2B-1 alumina based on the total weightof abrasive grain The portion of white fused aluminium oxide consists ofeach 28.6% by weight of FEPA grade F70 and F100, and 42.8% by weight ofFEPA grade F80 Mix 5 - Examples 3A-1, 30% by weight T and 70% by weightof white fused and 3B-1 aluminium oxide based on the total weight ofabrasive grain The portion of white fused aluminium oxide consists ofeach 28.6% by weight of FEPA grade F70 and F100, and 42.8% by weight ofFEPA grade F80 Mix 6 - Examples 1A-2, 100% by weight 80+ based on thetotal weight of abrasive and 1B-2, II-1, IV-1, V-3, grain IX-2 Mix 7 -Comparative 30% by weight Cerpass TGE ®, code TGE-0557, grit sizeExample Ref. 3A-1 100 and 70% by weight of white fused aluminium oxidebased on the total weight of abrasive grain The portion of white fusedaluminium oxide consists of each 28.6% by weight of FEPA grade F70 Mix8 - Comparative 100% by weight Cerpass TGE ®, code TGE-0557, grit sizeExample Ref. 3A-2 100 based on the total weight of abrasive grain Mix9 - Example II-1, 100% by weight white fused aluminium oxide based onthe Comparative Example total weight of abrasive grain, consisting of20% by weight Ref. II-2, Example IV-1, of FEPA grade F54, 50% by weightof FEPA grade F60, and Comparative Example IV- 30% by weight of FEPAgrade F70 2, Comparative Example Ref. V-5 Mix 10 - Comparative 30% byweight 3M ™ Ceramic Abrasive Grain 321 and 70% Example Ref. II-2, byweight of white fused aluminium oxide based on the total ComparativeExample weight of abrasive grain Ref. V-5 The 3M ™ Ceramic AbrasiveGrain 321 portion consists of 100% by weight of ANSI grade 60. Theportion of white fused aluminium oxide consists of each 28.6% by weightof FEPA grade F54 and F60, and 42.8% by weight of FEPA grade F70. Mix11 - Example III-1, 100% by weight 60+ based on the total weight ofabrasive VI-1, VII-1, VIII-1 grain Mix 12 - Comparative 30% by weight3M ™ Ceramic Abrasive Grain 321 and 70% Example Ref. III-2, by weight ofwhite fused aluminium oxide based on the total Comparative Exampleweight of abrasive grain Ref. VIII-2 The 3M ™ Ceramic Abrasive Grain 321portion consists of 100% by weight of ANSI grade 46. The portion ofwhite fused aluminium oxide consists of each 42.9% by weight of FEPAgrade F40 and F54, and 14.2% by weight of FEPA grade F46. Mix 13 -Comparative 20% by weight 3M ™ Ceramic Abrasive Grain 321 and 80%Example IV-2 by weight of white fused aluminium oxide based on the totalweight of abrasive grain The 3M ™ Ceramic Abrasive Grain 321 portionconsists of 100% by weight of ANSI grade 60. The portion of white fusedaluminium oxide consists of 25% by weight of FEPA grade F54, and of each37.5% by weight of FEPA grade F60 and F70. Mix 14 - Example V-1 30% byweight 80+ and 70% by weight white fused alumina by weight based on thetotal weight of abrasive grain The portion of white fused aluminiumoxide consists of each 50% by weight of FEPA grade F46 and F60 Mix 15 -Example V-1, 100% by weight white fused aluminium oxide based on theExample V-2, Example V-3 total weight of abrasive grain, consisting ofeach 35% by weight of FEPA grade F46 and F60, and 30% by weight of FEPAgrade F54. Mix 16 - Example V-2 50% by weight 80+ and 50% by weightwhite fused alumina by weight based on the total weight of abrasivegrain The portion of white fused aluminium oxide consists of 40% byweight of FEPA grade F46, and 60% by weight of FEPA grade F60 Mix 17 -Example V-4, 100% by weight white fused aluminium oxide based on theComparative Example total weight of abrasive grain, consisting of each20% by Ref. V-6, Example IX-1, weight of FEPA grade F70 and F100, and60% by weight of Example IX-2, FEPA grade F80. Comparative Example Ref.IX-3 Mix 18 - Comparative 30% by weight 3M ™ Ceramic Abrasive Grain 321and 70% Example Ref. V-6 by weight of white fused aluminium oxide basedon the total weight of abrasive grain The 3M ™ Ceramic Abrasive Grain321 portion consists of 100% by weight of ANSI grade 80. The portion ofwhite fused aluminium oxide consists of each 28.6% by weight of FEPAgrade F70 and F100, and 42.8% by weight of FEPA grade F80. Mix 19 -Comparative 5% by weight 3M ™ Ceramic Abrasive Grain 321, 25% by ExampleRef. VI-2 weight of Cerpass XTL ® code XTL-0560, 50% by weight ofmonocrystalline aluminium oxide, and 20% by weight of white fusedaluminium oxide based on the total weight of abrasive grain The 3M ™Ceramic Abrasive Grain 321 portion consists of 100% by weight of ANSIgrade 90. The Cerpass XTL ® code XTL-0560 portion consists of 100% byweight of ANSI grade 90. The monocrystalline aluminium oxide portionconsists of 100% by weight of FEPA grade F80. The white fused aluminiumoxide portion consists of 100% by weight of FEPA grade F70. Mix 20 -Example VII-2 30% by weight 60+ and 70% by weight white fused alumina byweight based on the total weight of abrasive grain The portion of whitefused aluminium oxide consists of 42.9% by weight of FEPA grade F24, and57.1% by weight of FEPA grade F30 Mix 21 - Comparative 30% by weightCerpass TGE ®, code TGE-0557, grit size 36 Example VII-3 and 70% byweight white fused alumina by weight based on the total weight ofabrasive grain The portion of white fused aluminium oxide consists of42.9% by weight of FEPA grade F24, and 57.1% by weight of FEPA grade F30Mix 22 - Example VIII-1, 100% by weight white fused aluminium oxidebased on the Comparative Example total weight of abrasive grain,consisting of each 30% by Ref. VIII-2 weight of FEPA grade F40 and F54,and 40% by weight of FEPA grade F46. Vitrified bond precursor Mix of98.5% by weight vitrified bond having a grain size of mix 97% <63 μm anda composition consisting of Na₂O, Al₂O₃, B₂O₃, and SiO₂, commerciallyavailable as vitrified bond VO 82069 from Reimbold & Strick, Germany and1.5% by weight of blue pigment, cobalt blue colour stain for glazesconsisting of CoAl₂O₄, commercially available as K90084 from Reimbold &Strick, Germany Temporary binder Consisting of Liquid temporary bindermix and solid temporary binder Liquid temporary binder Urea formaldehyderesin^(•), for example PA1175G available mix from PA resins AB, Sweden,now Chemoplastica AB, Sweden Solid temporary binder Potato starch^(•),for example Dextrin 20.912 available from Agrana Starke GmbH, AustriaPore inducing agent Naphthalene^(•), for example available from SintaSA, Belgium, in crystalline and sifted form; depending on the grain sizedistribution herein later referred to as Type A (212-500 μm) and Type B(300-1190 μm) ^(•)not present in the final product

Example I Outer Diameter (OD) Grinding

a. Manufacturing Process of Abrasive Grinding Wheels

Vitrified bonded abrasive grinding wheels having the same bond and wheeldimension of 500×25×304.8 mm (wheel diameter×thickness×bore diameter)and Ti shape (according to DIN:ISO 603:1999), i.e. a straight grindingwheel, were prepared according to the following manufacturing process:

(i) Mixing

The abrasive grain/grain mix as specified with respect to the exampleswas put into a mixing aggregate and the liquid temporary binder waspoured onto it while mixing. After stirring for about 3-5 minutes, amixture consisting of the vitrified bond precursor mix and the solidtemporary binder was added and the mixing was continued thoroughly forabout 10 minutes.

(ii) Sieving

With reference to the examples given, the mixture obtained in step (i)is screened with a sieve 16 mesh (mesh size 1.18 mm).

(iii) Moulding

The mixture obtained in step (ii) is put into a mould and formed bypressing to give green bodies. Typical forming pressures were 126-150kg/cm² for green bodies with an abrasive mix containing 100% 80+ and21-51 kg/cm² for green bodies with an abrasive mix containing 30% 80,60+ or T shaped abrasive grain.

(iv) Heat Treatment

With reference to the examples given, the achieved green bodies aredried at a temperature of 130° C. and sintered at a temperature of 930°C.

(vii) Finishing

The finishing operation comprises the grinding of the bore, the lateralsurfaces, and the peripheral surface.

TABLE 1 Characteristics of the test wheels of Example I Amounts [wt. %]*Comparative Comparative Comparative Comparative Example 1A- Example 2A-Example 3A- Example 1A- Example Ref. Example Ref. Example Ref. ExampleRef. 1 1 1 2 1A-2 2A-1 3A-1 3A-2 Green Structure Abrasive Mix 3 Mix 4Mix 5 Mix 6 Mix 1 Mix 2 Mix 7 Mix 8 Grain shaped 26.55 80+ 26.55 60+26.55 T 88.50 80+ abrasive grain 3M ™ 26.55 Ceramic grit 80, 90 AbrasiveGrain 321 Cerpass 26.55 88.50 TGE ®, grit 100 grit 100 code TGE- 0557White fused 61.95 61.95 61.95 — 88.50 61.95 61.95 — aluminium F70, 80,100 F70, 80, 100 F70, 80, 100 F70, 80, 100 F70, 80, 100 F70, 80, 100oxide Vitreous 11.50 11.50 11.50 11.50 11.50 11.50 11.50 11.50 bondTemporary binder Starch 0.50 0.50 0.50 0.50 0.50 0.50 0.50 .0.50 Liquid4.20 4.20 4.20 4.20 4.20 4.20 4.20 4.20 temporary binder mix Moulding2.110 2.110 2.110 2.110 2.110 2.110 2.110 2.110 density [g/cm³] WheelType** Type III Type III Type III Type III Type III Type III Type IIIType III Shape T1 T1 T1 T1 T1 T1 T1 T1 Dimension 500 × 25 × 500 × 25 ×500 × 25 × 500 × 25 × 500 × 25 × 500 × 25 × 500 × 25× 500 × 25 × 304.8304.8 304.8 304.8 304.8 304.8 304.8 304.8 Amounts [wt. %]* Example 1B-Example 2B- Example 3B- Example 1B- 1 1 1 2 Green Structure Abrasive Mix3 Mix 4 Mix 5 Mix 6 Grain shaped 25.97 80+ 25.97 60+ 25.97 T 86.58 80+abrasive grain 3M ™ Ceramic Abrasive Grain 321 White fused 60.61 60.6160.61 aluminium F70, 80, 100 F70, 80, 100 F70, 80, 100 oxide Vitreousbond 13.42 13.42 13.42 13.42 Temporary binder Starch 0.85 0.85 0.85 0.85Liquid 3.30 3.30 3.30 3.30 temporary binder mix Moulding 2.150 2.1502.150 2.150 density [g/cm³] Wheel Type** Type VII Type VII Type VII TypeVII Shape T1 T1 T1 T1 Dimension 500 × 25 × 500 × 25 × 500 × 25 × 500 ×25 × 304.8 304.8 304.8 304.8 **Here and in the following the Wheel Type(or the abrasive article or tool type) relates to the hardness/structureof the test abrasive tools and had been classified as a type rangingfrom Type I (lower volume percentage of bond and abrasive grain, andhigher volume percentage of porosity) to Type XI (higher volumepercentage of bond and abrasive grain, and lower volume percentage ofporosity) based on the percentage of bond and porosity in the abrasivetools (for example wheels or segments), with a higher volume percentageof bond corresponding to a higher type and a more rigid or hard abrasivetool. For example with specific reference to Example 1, i.e. Type III orType VII, test wheels of Type VII can be considered as acting harder ormore rigid under the grinding conditions used as compared to test wheelsof Type III because of the higher volume percentage of bond and lessporosity present in wheels of Type VII. *weight amounts of the greenwheels before firing

B. Testing Procedure

The grinding wheels prepared as in Example I were tested in acylindrical grinding application in order to establish the grindingperformance of the wheels. The grinding tests were performed using thefollowing grinding conditions:

-   Grinding Process: outer diameter (OD-) grinding-   Machine: UVA Johansson 10MD; 18.5 kW, year of construction 1979    (rebuilt)-   Workpiece: bearing steel; Ovako 824, Ovako Hofors AB, Sweden 1.3537    (100CrMo7) according to EN ISO 683-17:1999, 62-64 HRc, diameter 100    mm, length 20 mm-   Parameters: operating speed of grinding wheel: 45 m/s; wet grinding    using Cimtech D18 (3%) as a lubricant/coolant-   Dressing: Multi-point diamond dresser, V448-0,8x4-4 bars, Kucher    GmbH, Germany, synthetic diamond, width 15 mm, length 28 mm,    traverse speed 350 mm/min

Using the grinding wheels of Example I, three sets of grinding testswere performed.

Test Series (I) used a specific material removal rate of Q′_(W) 2.5min³/mm/s (infeed: 0.006 mm/turn of work piece; peripheral speed of workpiece: 25 m/min).

Test Series (II) used more severe grinding conditions by applying aspecific material removal rate of Q′_(W) 5 mm³/mm/s (infeed: 0.010mm/turn of work piece; peripheral speed of work piece: 30 m/min).

Test series (III), using a specific material removal rate of Q′_(W) 2.5mm³/mm/s (infeed: 0.006 mm/turn of work piece; peripheral speed of workpiece: 25 m/min) to remove 1.2 mm of work piece in radius following by 5s of outspark was chosen to characterise the surface quality of the workpiece.

The power drawn was recorded as a function of the grinding time. Theresults of Test Series (I) are shown in FIG. 1 and FIG. 2. The resultsof Test Series (II) are shown in FIG. 3 and FIG. 4.

Typically grinding curves of this type are cyclical: The power drawn(kilowatts) increases over time as the grinding forces increase. Whenthe forces get high enough the wheel breaks down, breaking and ejectinggrit particles and then the grinding power consumption (grinding force)decreases. At this point dressing of the grinding wheel has to be set upin order to avoid defects at the workpiece to be abraded and in order toprovide for constant abrading performance of the grinding wheel. Thenthe grinding cycle has to be started again. What is desired is agrinding wheel having a long cycle period (in terms of constant powerdrawn), indicating good form holding and long total service life of thewheel.

For each wheel the grinding test was operated until the powerconsumption fell below the power consumption at the initial grindinglevel. This was considered the test endpoint. Due to their long servicelife the tests of Test Series (I) using the wheels of all examplesexcluding Example Ref. 1A-2 and Ref. 2A-1, and the tests of Test Series(II) using the grinding wheels of Examples 1A-2 and 1B-2 (100% 80+) wereended before reaching this point.

In addition, the mean value of surface roughness R_(a) of the workpieceafter the grinding according to Test Series III has been determined witha device of type SURFTEST SJ-210 of Mitutojo. The results of the TypeIII-wheels are summarized in FIG. 5.

C. Results

A comparison of the results obtained under Test Series I and II showsthe higher grinding performance of the examples given by increasing thespecific material removal rate (FIG. 1-4). While in Test Series I(Q′_(w) 2.5 mm³/mm/s) all variants comprising non-seeded sol-gel derivedaluminium oxide refer to a long service life (FIG. 1 and FIG. 2,examples excluding the Comparative Examples Ref. 1A-2, Ref. 2A-1, Ref3A-1, and Ref. 3A-2), differences in the power drawn can be seen in FIG.3 and FIG. 4 when applying the grinding conditions of Test Series IIcomprising a specific material removal rate Q′_(W) of 5 mm³/mm/s.

FIG. 3 and FIG. 4 illustrate a marked increase in the period of thegrinding cycle when using grinding wheels containing shaped abrasiveparticles in accordance with the present invention in comparison to thevariants comprising white fused aluminium oxide or 3M™ Ceramic AbrasiveGrain 321 or extruded Cerpass TGE® (Comparative Examples Ref. 1A-2 orRef. 2A-1, or Ref. 3A-1) respectively, and confirm the increase in theservice life. For example, the period for the grinding cycle of Example1A-1 in comparison to Ref. 2A-1 is nearly doubled, thus resulting in alonger dressing interval. Considering grinding wheels with abrasivemixes consisting of 100% shaped abrasive particles in accordance withthe present invention (Example 1A-2) as well as 100% extruded CerpassTGE® (Comparative Example Ref. 3A-2) Example 1A-2 shows a markedincrease in service life. The testing of Example 1A-2 was terminatedartificially because of the constant power drawn during a certaingrinding duration.

With reference to the examples comprising shaped abrasive particles inaccordance with the present invention an influence of the abrasive grainsize and the amount of the abrasive grain portion can be seen.Increasing the abrasive grain portion effects longer service life. Thiscan be seen from Examples 1A-2 and 1B-2 in comparison to examples 1A-1and 1B-1, each containing shaped abrasive particles 80+. Using the sameportion of the shaped abrasive particle of the invention, examples 2A-1and 2B-1, containing shaped abrasive particles 60+, show the influenceof the grain size and an increase of the service life by reducing thewear of the shaped abrasive particles in comparison to the Examples 1A-1and 1B-1, comprising shaped abrasive particles 80+.

In sum, the use of shaped abrasive grains in a vitrified bond canprovide abrasive grinding wheels exhibiting a long and stable grindingcurve in grinding applications, particularly under more severe grindingconditions, as for example shown in Test Series II. Surprisingly, theservice life of the wheels increased when tested using a higher specificremoval rate (Q′_(w)=5.0 mm³/mm/s). Increasing the amount of shapedabrasive particles according to the present invention can provide anextremely long grinding cycle.

In addition, the use of shaped abrasive grains has been found to provideimproved surface finish as evident from a comparison of the examples forwheels of Type III given and shown in FIG. 5. With respect to thegrinding practice, it has to be stated that deviation of the results islow. Because of its narrow range the results of the mean value ofsurface roughness R_(a) are not described in detail.

With respect to the results obtained it is also to be noted that thegrinding tests involved a specific grinding machine built in 1979. Theuse of a more recently constructed machine is expected to provide evenbetter results since higher values for Q′w could be accomplished.

Example II Outer Diameter (OD) Grinding A. Manufacturing Process ofAbrasive Grinding Tools

Vitrified bonded abrasive grinding wheels having composition, type,dimension (wheel diameter×thickness×bore diameter), shape and bond asdescribed in Table 2 were prepared as described in Example I.

TABLE 2 Characteristics of Grinding Wheels used in Example IIComparative Example II-1 Example Ref. II-2 Green Structure Rim CenterRim Center Abrasive Grain Mix 6 Mix 9 Mix 10 Mix 9 Shaped abrasive 88.50grain 80+   3M ™ Ceramic 26.55 Abrasive Grain Grit 60 321 White fused88.50 61.95 88.50 alumina F54, 60, 70 F54, 60, 70 F54, 60, 70 Vitreousbond 11.50 11.50 11.50 11.50 Starch  1.50 1.50 1.00 1.00 Liquidtemporary  4.24 4.24 3.89 3.89 binder mix Pore inducing 13.27 13.2713.27 13.27 agent (Type A) (Type A) (Type A) (Type A) Moulding density 2.100 2.100 2.010 2.010 [g/cm³] Wheel Wheel Type** Type IV Type V ShapeT5 T5 Dimension 750 × 100 × 750 × 100 × 304.8-1-420 × 30 304.8-1-420 ×30 **(see Table 1)

B. Testing Procedure

The grinding wheels prepared as in Example II were tested in an outerdiameter (OD) grinding application in order to establish the grindingperformance of the wheels.

Using the grinding wheels of Example II, grinding tests were performedusing the following grinding conditions:

-   Grinding Process: outer diameter (OD-) grinding-   Machine: HOL-MONTA 2000CNC (22 kW)-   Workpiece: pressure cylinder, diameter 620 mm, length 1110 mm,    hard-chrome plated; required surface roughness R_(z)<4 μm (R_(z)    describing the average roughness depth)-   Parameters: Roughing via plunge grinding; 10 plunges, speed ratio    q_(s) 67 and finishing via traverse grinding, speed ratio q_(s) 67,    speed of flunge speed rate v_(f) 700 mm/min-   Dressing: Multi-point diamond dresser MKD4x0,8

C. Results

TABLE 3 Results of Exampe II Q′_(w) grinding Q′_(w) Semi- Q′_(w) stockv_(w) v_(c) Roughing roughing Finishing [mm] [rpm/min] [m/s] [mm³/mm/s][mm³/mm/s] [mm³/mm/s] Dressing Comparative Example Roughing 0.5  11 251.8 0.9 0.25 after each Ref. II-2 plunge, 4 × 0.02 mm Finishing 0.04 1125 2   2   0.2  1× before grinding, 4 × 0.02 mm Example II-1: Test 1Roughing 0.5  I 1 25 1.8 0.9 0.25 after each plunge, 4 × 0.02 mmFinishing 0.04 11 25 2   2   0.2  1× before grinding, 4 × 0.02 mmExample II-1: Test 2 Roughing 0.5  12 27 2.3 1.3 0.6  after each 2^(nd)plunge 4 × 0.01 mm Finishing 0.04 11 25 2   2   0.2  1× before grinding4 × 0.01 mm Example II-1: Test 3 Roughing 0.9  12 27 2.9 1.5 0.8  aftereach 2^(nd) plunge 4 × 0.01 mm Finishing 0.04 11 25 2   2   0.2  l×before grinding 4 × 0.01 mm

The grinding tests were performed in test series using three differentparameter sets for the roughing and the same parameter sets for thefinishing process. The parameter sets are summarized in Table 3. Theresults show an increase in the performance thus reflected by thespecific material removal rate Q′_(W) and the total grinding time forthe test wheel as well as an improvement in the dressing process byreducing the dressing amounts by 50%. Considering the total grindingtime the reference wheel as well as the test wheel using the parameterset of Test 1 show total grinding times of 270 minutes. Using parameterset of Test 2 enables to reduce the grinding time to 190 minutes (−30%)and to increase the infeed by 29% in comparison to the reference wheeland Test 1. Test 3 comprised a 80% higher grinding stock and a 40%higher infeed. Even with these more severe conditions present thegrinding time was increased by only 10% (210 minutes) than in. Test 2and still was ca. 20% shorter than in Test 1. In all test series thetest wheel met the required surface quality and gained a silk-matsurface quality.

Example III Outer Diameter (OD) Grinding A. Manufacturing Process ofAbrasive Grinding Tools

Vitrified bonded abrasive grinding wheels having composition, type,dimension (wheel diameter×thickness×bore diameter), shape and bond asdescribed in Table 4 were prepared as described in Example I.

TABLE 4 Characteristics of Grinding Wheels used in Example IIIComparative Example Ref. Green Structure Example III-1 III-2 AbrasiveGrain Mix 11 Mix 12 Shaped abrasive grain 85.10 60+   3M ™ CeramicAbrasive Grain 25.53 321 Grit 46 White fused alumina 59.57 F40, 46, 54Vitreous bond 14.90 14.90 Starch  1.50 1.50 Liquid temporary binder mix 4.92 4.92 Pore inducing agent 12.77 12.77 (Type A) (Type A) WheelMoulding density [g/cm³]  2.450 2.360 Wheel Type** Type X Type XI ShapeT1 T1 Dimension 250×9×85 250×9×85 **(see Table 1)

B. Testing Procedure

The grinding wheels prepared as in Example III were tested in an outerdiameter (OD) grinding application in order to establish the grindingperformance of the wheels.

Using the wheels of Example III, grinding tests were performed using thefollowing grinding conditions:

-   Grinding Process: outer diameter (OD-) grinding; semi-finish    sidegrinding of chrome plated slots-   Machine: Chris Marie, adopted to customer needs-   Workpiece: vessel engine piston with diameter 460 mm, 4 slots per    piston-   Parameters: semi finish side-grinding of chrome plated slots, 4    slots per piston; stock removal: 0.3-0.5 mm per side-   Dressing: Multi-point diamond dresser MKD4x0,8

C. Results

TABLE 5 Results of Example III Comparative Example Ref. III-2 ExampleIII-1 Total infeed [mm] 0.43 0.30 Effective take of material per 0.230.25 slot [mm] Dressing 9 times 0.01 mm 2 times 0.01 mm Dressing withoutinfeed, to 6 times 4 times open the wheel again Grinding time per side[min] 20 11

Using the same parameter sets the test wheel gains improvements withregard to the grinding time as well as to the dressing process asfollows:

The grinding time was reduced by 9 minutes per side, each slot showingtwo sides this results in a 72 minutes decrease of the grinding time perpiston (4 slots per piston). In comparison to the reference wheel thegrinding time can be reduced almost by 50%.

Considering the dressing process 7 dressing cycles less were necessaryfor the test wheel. Calculating the total dressing amount for both sidesof all slots (2 sides each slot, 4 slots) leads to 0.56 rum less wheelusage.

Example IV Outer Diameter (OD) Grinding A. Manufacturing Process ofAbrasive Grinding Tools

Vitrified bonded abrasive grinding wheels having composition, type,dimension (wheel diameter×thickness×bore diameter), shape and bond asdescribed in Table 6 were prepared as described in Example I.

TABLE 6 Characteristics of Grinding Wheels used in Example IVComparative Green Example IV-1 Example Ref. IV-2 Structure Rim CenterRim Center Abrasive Mix 6 Mix 9 Mix 13 Mix 9 Grain Shaped 87.72 abrasivegrain 80+   3M ™ Ceramic 17.54 Abrasive Grit 60 Grain 321 White fused87.72 70.18 87.72 alumina F54, 60, F54, 60, 70 F54, 60, 70 70 Vitreousbond 12.28 12.28 12.28 12.28 Starch  0.80 0.80 0.80 0.80 Liquid  3.123.12 3.12 3.12 temporary binder mix Moulding  2.300 2.300 2.190 2.190density [g/cm³] Wheel Wheel Type** Type IX Type VII Shape T5N T5NDimension 610 × 100 × 610 × 100 × 304.8-1-390 × 50 304.8-1-390 × 50**(see Table 1)

B. Testing Procedure

The grinding wheels prepared as in Example IV were tested in an outerdiameter (OD) grinding application in order to establish the grindingperformance of the wheels.

Using the wheels of Example IV, grinding tests were performed using thefollowing grinding conditions:

-   Grinding Process: outer diameter (OD-) grinding-   Machine: Schaudt FlexGrind M-   Workpiece: drive shaft showing diameter 170 mm, 140 mm, and 160 mm,    case hardened to 60-62 HRc; material: 17CrNiMo6; required surface    quality R_(a) 0.8 μm-   Parameters: see Table 7; grinding stock 1 mm; dressing every 2 parts    one stroke-   Dressing: Diamond dresser CVD 1.0×1.0×4 D (one rod)

C. Results

TABLE 7 Results of Example IV Infeed Grinding Infeed semi- Infeed timev_(c) roughing roughing finishing Speed roughing Q′_(w) [m/s] [mm/min][mm/min] [mm/min] ratio q_(s) [min:sec] [mm³/mm/s] R_(a) [μm]Comparative Example Ref. Ø170 k6 45 0.2584 0.0861 0.0215 92 05:08 2.20.647 Ref. IV-2 Mix f2 Ref. Ø140 k6 45 0.3137 0.1046 0.0261 95 2.3 Mixf2 Ref. Ø160 h11 45 0.2628 0.1314 0.0788 90 2.3 Mix f2 Example IV-1:Test 1 Mix f1 Ø170 k6 45 0.2584 0.0861 0.0215 92 05:08 2.2 0.602 Mix f1Ø140 k6 45 0.3137 0.1046 0.0261 95 2.3 Mix f1 Ø160 h11 45 0.2628 0.13140.0788 90 2.3 Example IV-1: Test 2 Mix f1 Ø170 k6 63 0.5610 0.13500.0330 60 01:32 5   0.466 Mix f1 Ø140 k6 63 0.6820 0.1600 0.0400 60 5  0.38  Mix f1 0160 h11 63 0.5960 0.1430 0.0788 60 5   0.337 Example IV-1:Test 3 Mix f1 Ø170 k6 63 0.8988 0.1350 0.0330 60 8   Mix f1 Ø140 k6 631.0913 0.1600 0.0400 60 8   Mix f1 Ø160 h11 63 0.9549 0.1430 0.0788 608  

The tests were performed in three test series using different parametersets. Test 1 applying the same parameter set as for the referenceresults in a better surface quality represented by the mean value ofsurface roughness R_(a). The results of Test 2 and Test 3 show that thetest wheel enables an increase in the operating speed v_(c), as well ashigher infeed rates for each machining step thus resulting in a markedincrease in the specific material removal rate Q′_(W) and in ca. 70%shorter grinding times as described for the roughing. The surfacequality generally improves using the test specification and results in areduction of the mean surface roughness R_(a) by 50%.

Example V Single Rib Gear Grinding A. Manufacturing Process of AbrasiveGrinding Wheels

Vitrified bonded abrasive grinding wheels having composition, type,dimension (wheel diameter×thickness×bore diameter), shape and bond asdescribed in Table 8 were prepared as described in Example I:

B. Testing Procedure

The grinding wheels prepared as in Example V were tested in a single ribgear grinding application in order to establish the grinding performanceof the wheels.

Using the wheels of Example V, two sets of grinding tests were performedusing the following grinding conditions:

Test 1:

-   Grinding Process: single rib gear grinding-   Grinding tool: T1ESP 400×60×127 V=50°, U=15-   Machine: Hofler Rapid 2500 (37 kW)-   Workpiece: Planet gear, normal module 13.5 mm, pressure angle: 20°,    helix angle: 7.25°, number of teeth: 50, face width 380 mm;    Material: 18CrNiMo7-6 case hardened to 62 HRc-   Parameters: operating speed v_(c) of grinding wheel: 30 m/s

Test 2:

-   Grinding Process: single rib gear grinding-   Grinding Tool: T1ESP 400×50×127 V=65° U=12-   Machine used: Hofler Rapid 1250 (24 kW)-   Workpiece: Planet gear, normal module 13.5 min, pressure angle: 20°,    helix angle: 7°, number of teeth: 43, face width 250 mm; Material:    17CrNiMo6 Planet gear, normal module 16 mm, pressure angle: 20°,    helix angle: 6.25°, number of teeth: 31, face width 371.2 mm;    Material: 18CrNiMo7-6 case hardened to 62 HRc, required mean value    of surface roughness R_(a) 0.4 μm (both workpieces)-   Parameters: operating speed v_(c) of grinding wheel: 30 m/s

TABLE 8 Characteristics of the test wheels of Example V Example V-1Example V-2 Example V-3 Green Structure Rim Center Rim Center Rim CenterAbrasive Grain Mix 14 Mix 15 Mix 16 Mix 15 Mix 6 Mix 15 Shaped 27.5245.87 91.74 abrasive 80+ 80+ 80+ grain 3M ™ Ceramic Abrasive Grain 321White fused 64.22 91.74 45.87 91.74 91.74 alumina F46, 60 F46, F46, 60F46, F46, 54, 54, 60 54, 60 60 Vitreous bond 8.26 8.26 8.26 8.26 8.268.26 Starch 2.10 2.10 2.10 2.10 2.10 2.10 Liquid 3.37 3.37 3.37 3.373.37 3.37 temporary binder mix Pore 9.17 9.17 9.17 9.17 9.17 9.17inducing (Type A) (Type A) (Type A) (Type A) (Type A) (Type A) agentMoulding 2.090 2.090 2.090 2.090 2.090 2.090 density [g/cm³] Wheel WheelType Type IV Type IV Type IV ** Shape T1ESP T1ESP T1ESP Dimension 400 ×50 × 127 V 400 × 50 × 127 V 400 × 50 × 127 V 65°, 65°, U = 12 65°, U =12 U = 12 (Test 2) (Test 2) (Test 2) 400 × 60 × 127 V 50°, U = 15(Test 1) Comparative Comparative Example V-4 Example Ref. V-5 ExampleRef. V-6 Green Structure Rim Center Rim Center Rim Center Abrasive GrainMix 3 Mix 17 Mix 10 Mix 9 Mix 18 Mix 17 Shaped 27.40 abrasive 80+ grain3M ™ 27.52 27.3 Ceramic Grit 60 Grit 80 Abrasive Grain 321 White fused63.92 91.32 64.22 91.74 63.92 91.32 alumina F70, F70, F54, 60, F54, F70,80, F70, 80, F80, 80, 100 70 60, 70 100 100 F100 Vitreous bond 8.68 8.688.26 8.26 8.68 8.68 Starch 1.62 1.62 1.60 1.60 1.62 1.62 Liquid 3.013.01 3.49 3.49 3.01 3.01 temporary binder mix Pore 18.26 18.26 18.3518.35 18.26 18.26 inducing (Type B) (Type B) (Type B) (Type B) (Type B)(Type B) agent Moulding 1.980 1.980 2.020 2.020 1.980 1.980 density[g/cm³] Wheel Wheel Type Type IV Type IV Type IV ** Shape T1ESP T1ESPT1ESP Dimension 400 × 50 × 127 V 50°, 400 × 50 × 127 V 50°, 400 × 50 ×127 V 65°, U = 15 (Test 1) U = 12 (Test 2) U = 12 (Test 2) **(see Table1)

C. Results

TABLE 9A Results of Test 1 - Test series A Comparative Example Ref. V-5Example V-4 Example V-3 Specific material removal 16 24 30 rate Q′_(W)[mm³/mm/s] Specific chip volume V′_(W) 10.000 15.000 18.000 [mm³/mm]Mean value of surface 0.40 0.30 0.30 roughness R_(a) [μm]

TABLE 9B Results of Test 1 - Test series B showing a specific materialremoval rate Q′_(W) of 16 mm³/mm/s Comparative Example Ref. V-5 ExampleV-4 Example V-3 Specific material removal 16 16 16 rate Q′_(W)[mm³/mm/s] Specific chip volume V′_(W) 10.000 18.000 30.000 [mm³/mm]

TABLE 9C Results of Test 2 Comparative Example Ref. Example ExampleExample V- V-6 V-1 V-2 3 Specific material 14 24 30 30 removal rateQ′_(W) [mm³/mm/s] Specific chip 800 1500 2500 2500 volume V′_(W)[mm³/mm] Comment: Too less machine power

The test series show an increase in the specific material removal rateQ′_(W) as well as in the specific chip volume V′_(W) for the test wheelsin comparison to the reference wheels independent from the workpiecematerial type and dimensions. In Test 2 the machine used had too lessmachine power to increase both parameters for Example V-3. In general itcan be seen that the increase depends on the amount of shaped abrasiveparticles resulting in the highest values for an abrasive fractionentirely consisting of shaped abrasive particles (Example V-3). Using anamount of 30% of shaped abrasive grain (Example V-1 and Example V-4)results in an increase in the specific chip volume V′_(W) in the rangeof 50-90% and an increase of the specific material removal rate Q′_(W)in the range of 50-70%. Increasing the amount of shaped abrasive grainto 50% (Example V-2) gains an increase by ca. 210% for the specific chipvolume and ca. 1.15% for the specific material removal rate. Keeping thespecific material removal rate Q′_(W) constant, in comparison to thereference grinding wheel Comparative Example Ref. V-5 Test Series B ofTest 1 shows an increase in the specific chip removal of 80% for ExampleV-4 and of 200% for Example V-3, thus resulting in longer dressingcycles, less redressing and proving the excellent form and profileholding of the test grinding wheels. Even under these severe grindingconditions no workpiece burning or discoloration was observed.Considering the surface quality of the workpieces an improvement can beseen related to the test wheels of Test 1 (Test Series A) thus reflectedby the mean value of the surface roughness R_(a) and its decrease by 25%with regard to the reference wheel. The test series document thebeneficial effects of abrasive tools consisting of shaped abrasive grainreferring to high performance grinding and combined with highlyefficient process and tool economics.

Example VI Generating Gear Grinding A. Manufacturing Process of AbrasiveGrinding Tools

Vitrified bonded abrasive grinding wheels having composition, type,dimension (wheel diameter×thickness×bore diameter), shape and bond asdescribed in Table 10 were prepared as described in Example I.

TABLE 10 Characteristics of Grinding Wheels used in Example VIComparative Example Ref. Green Structure Example VI-1 VI-2 AbrasiveGrain Mix 11 Mix 19 Shaped abrasive grain 86.58 60+   3M ™ Ceramic 4.45Abrasive Grain 321 grit 90 Cerpass XTL ®, 22.25 code 0560 Grit 90 Singlecrystal alumina 44.5 F80 White fused alumina 17.8 F70 Vitreous bond13.42 11.00 Starch  1.20 0.96 Liquid temporary  4.56 3.29 binder mixPore inducing agent 12.99 6.05 (Type A) (Type A) Moulding density  2.0402.125 [g/cm³] Wheel Wheel Type** Type IX Type VII Shape T1SP T1SPDimension 320 × 230 × 110 mm 320 × 230 × 110 mm modulus 9.0 mm, modulus9.0 mm, pressure angle 20°, 2 pressure angle 20°, 2 starts starts **(seeTable 1)

B. Testing Procedure

The grinding wheels prepared as in Example VI were tested in agenerating gear grinding application in order to establish the grindingperformance of the wheels. Using the wheels of Example VI, grindingtests were performed using the following grinding conditions

-   Grinding Process: Generating gear grinding using so-called grinding    worms-   Machine used: Liebherr LCS1200 (35 kW)-   Work piece: Helical gear, normal module 9 mm, pressure angle: 20°,    helix angle: 10°, number of teeth: 65, face width 153 mm; Material:    18CrNiMo6-7, case hardened to 58 HRc-   Parameters: operating speed v_(c) of grinding wheel: 59 m/s

C. Results

TABLE 11 Results of Example VI Specific material Material removalremoval rate Infeed Feed rate rate Q′W roughing roughing Q_(max) [mm³/radial [mm] [mm/rpm] Shifting [mm³/s] mm/s] Comparative 0.34 0.45diagonal 267 6.5 Example Ref. VI-2 Example 0.34 0.45 diagonal 269 6.5VI-1: Test 1 Example 0.34 0.75 diagonal 475 10.2 VI-1: Test 2 Example0.34 1.00 diagonal 502 13.6 VI-1; Test 3 Example 0.34 1.30 diagonal 77217.7 VI-1: Test 4 Example 0.45 1.20 diagonal 883 21.0 VI-1: Test 5

The tests were performed in five test series using different grindingparameters thus described by the infeed and the feed rate for theroughing process. Varying the feed rate shows an increase in thespecific material removal rate Q′_(W) in the range of 55-170%.Increasing the feed rate as well as the infeed results in a markedincrease in the specific material removal rate Q′_(W) with regard to thereference wheel thereby reducing the process consisting of threeroughing steps by one roughing step thus effecting the total grindingtime. Even under these severe conditions the test wheel showed noclogging.

Example VII Surface Grinding with Segments A. Manufacturing Process ofAbrasive Grinding Tools

Vitrified bonded abrasive grinding segments having composition, type,dimension (segment width B×thickness C×length L), shape and bond asdescribed in Table 12 were prepared as described in Example I.

TABLE 12 Characteristics of Grinding Segments used in Example VIIComparative Green Structure Example VII-1 Example VII-2 Example Ref.VII-3 Abrasive Grain Mix 11 Mix 20 Mix 21 Shaped abrasive 91.74  27.52 grain 60+   60+   Cerpass TGE ®, 27.3 code 0557 Grit 36 White fused64.22  63.7 alumina F24, F30 F24, F30 Vitreous bond 8.26 8.26 9.00Starch 1.50 1.50 1.74 Liquid temporary 3.85 3.85 3.67 binder mix Poreinducing 13.76  13.76  15.00 agent (Type B) (Type B) (Type B) Mouldingdensity  2.080  2.080 2.070 [g/cm³] Segments Abrasive tool Type II TypeIl Type II Type** Shape T3101 T3101 T3101 Dimension 120 × 40 × 200 120 ×40 × 200 120 × 40 × 200 **(see Table 1)

B. Testing Procedure

The segments prepared as in Example VII were tested in surface grindingapplication in order to establish the grinding performance of thesegments. Using the segments of Example VII, grinding tests wereperformed using the following grinding conditions:

-   Grinding Process: surface grinding-   Machine: Kehren D15CNC (110 kW), Table diameter 1500 mm, grinding    head diameter 800 mm (applying 14 segments T3101-120×40×200)-   Workpiece: Die plate, 546×696×66.95 mm, Material: 1.2085 (soft, high    chrome content 16-17%)-   Parameters: operating speed v_(c) 800 rpm, feed rate v_(w) 15 rpm,    grinding stock, 0.3 mm, traverse speed of (see Table 13)-   Dressing: Multipoint diamond dresser, 16 mm

C. Results

TABLE 13 Results of Example VII Total Grinding v_(f)1 v_(f)2 v_(f)3 Weartime [mm/min] [mm/min] [mm/min] R_(a) [μm] [mm] [min:sec] Example VII-1Test 1 0.15 0.15 0.10 0.97 0.28 07:10 Test 2 0.30 0.30 0.10 1.1  0.3305:45 Test 3 0.30 0.30 0.10 1.0  0.39 06:15 Test 4 0.50 0.50 0.10 0.970.36 06:05 Example VII-2 Test 1 0.15 0.15 0.10 1.9  0.35 07:45 Test 20.30 0.30 0.10 1.4  0.50 07:30 Test 3 0.15 0.15 0.10 1.3  0.28 07:30Test 4 0.15 0.15 0.10 0.25 08:00

The tests were performed in comparison to a reference segment comprisingextruded abrasive rods using different parameter sets. For the referenceconditions as in Test 1 were chosen. In general the traverse speed wasincreased from 0.15 to 0.30, and 0.50 mm/min, respectively. With themachine table present the reference set of segments was able to grindtwo die plates simultaneously in a total grinding time of 10-12 minutes.Considering the corresponding set of test segments four die plates couldbe ground simultaneously in ca. 6 minutes (Mix f1, ca. −50%) and ca.7.5-8 minutes (Mix f2, ca. −30%). The wear of the tests segments wasreduced to 0.3-0.4 mm (ca. −35%) in comparison to the reference segmentsshowing a wear of 0.4-0.7 mm. In comparison to the reference segments noclogging of the test segments was observed. The workpiece showedsilk-mat surface quality. In general the test series resulted in amarked improvement with regard to the efficiency of the entire grindingprocess.

Example VIII Surface Grinding—Reciprocating Method A. ManufacturingProcess of Abrasive Grinding Tools

Vitrified bonded abrasive grinding wheels having composition, type,dimension (wheel diameter×thickness×bore diameter), shape and bond asdescribed in Table 14 were prepared as described in Example I.

TABLE 14 Characteristics of Grinding Wheels used in Example VIIIComparative Example VIII-1 Example Ref. VIII-2 Green Structure RimCenter Rim Center Abrasive Mix 11 Mix 22 Mix 12 Mix 22 Grain Shaped92.17  abrasive 60+   grain 3M ™ 26.79 Ceramic grit 46 Abrasive Grain321 White fused 92.17 62.51 89.30 alumina F40, 46, 54 F40, 46, 54 F40,46, 54 Vitreous 7.83 7.83 10.70 10.70 bond Starch 2.10 2.10 1.25 1.25Liquid 3.57 3.57 3.86 3.86 temporary binder mix Pore 13.82  13.82 17.8617.86 inducing (Type A) (Type A) (Type B) (Type B) agent Moulding  2.2402.240 2.050 2.050 density [g/cm³] Wheel Wheel Type** Type I Type IVShape T26 T26 Dimension 400 × 100/6 × 400 × 100/6 × 127-2-200 × 25/11 A= 2 127-2-200 × 25/11 A = 2 **(see Table 1)

B. Testing Procedure

The grinding wheels prepared as in Example VIII were tested in areciprocating grinding application in order to establish the grindingperformance of the wheels. Using the wheels of Example VIII, grindingtests were performed using the following grinding conditions

-   Grinding Process: reciprocating grinding-   Machine: Rosa Linea Avion 13.7 P (17 kW)-   Workpiece: customer-specific component; type of material: GGG60;    required mean value of surface roughness R_(a) 1.8 mm-   Parameters: Roughing via plunge grinding and finishing via    reciprocating grinding; operating speed v_(c) and other grinding    parameters (see Table 14)-   Dressing: multipoint diamond dresser

C. Results

TABLE 15 Results for Example VIII Counts Grinding Infeed/ Speed Specificmaterial Surface of v_(c) Infeed stock pass ratio removal rate Q′_(w)Roughness Process passes [m/s] [mm/min] [mm] [mm] q_(s) [mm³/mm/s] R_(z)[μm] Comparative Roughing 3× 32 16000 0.8  0.007 120 2   Example Ref.VIII-2 Finishing 1× 32 16000 0.03 0.005 120 1.4 6.33 Example VIII-1:Roughing 3× 32 16000 0.8  0.007 100 2   Test 1 Finishing 1× 32 160000.03 0.005 100 1.4 3.94 Example VIII-1: Roughing 3× 32 16000 0.8  0.014100 4   Test 2 Finishing 1× 27 16000 0.03 0.005 100 1.4 3.33 ExampleVIII-1: Roughing 3× 27 16000 0.8  0.020 100 5.3 Test 3 Finishing 1× 2716000 0.03 0.005 100 1.4 5.64

The results are shown for the roughing as well as for the finishingprocess. The roughing process was investigated by three test seriesusing different grinding parameters. The parameter set for the finishingprocess was kept as for the reference wheel. Performing the tests withthe same parameter set as for the reference wheel gains a higher surfacequality as for the reference, represented by a lower value for theaverage roughness depth R_(z) which means a mean value for the surfaceroughness of 0.64 μm for Test 1. In Test 2 and Test 3 the infeed perpass was increased by 100-185% resulting in 100-165% higher specificmaterial removal rates Q′ w and for Test 2 in a further improvement ofthe surface quality of the workpiece (R_(a) 0.49 μm) in comparison tothe reference test. Even under the grinding conditions of Test 3a bettersurface quality (R_(a) 0.88 μm) was obtained than with the referencewheel. Additionally it was observed that the reference wheel showedclogging and the workpiece became unusually warm during grinding.Considering all test series the test wheel does not show this behavior.The dressing after each plunge of the roughing process was reduced todressing after the third plunge thus leading to an increase inefficiency of the entire grinding process.

Example IX Surface Grinding—Creep-Feed Grinding A. Manufacturing Processof Abrasive Grinding Tools

Vitrified bonded abrasive grinding wheels having composition, type,dimension (wheel diameter×thickness×bore diameter), shape and bond asdescribed in Table 16 were prepared as described in Example I.

TABLE 16 Characteristics of Grinding Wheels used in Example IX Example1X-1 Example 1X-2 Comparative Example Ref. IX-3 Green Structure RimCenter Rim Center Rim Center Abrasive Grain Mix 3 Mix 17 Mix 6 Mix 17Mix 2 Mix 17 Shaped abrasive grain 26.32 87.72 80+ 80+ 3M ™ CeramicAbrasive 26.32 Grain 321 Grit 80, 90 White fused alumina 61.40 87.7287.72 61.40 87.72 F70, 80, 100 F70, 80, 100 F70, 80,100 F70, 80, 100F70, 80, 100 Vitreous bond 12.28 12.28 12.28 12.28 12.28 12.28 Starch1.10 1.10 1.50 1.50 1.10 1.10 Liquid temporary binder mix 3.93 3.93 4.744.74 3.93 3.93 Pore inducing agent 21.93 21.93 13.82 13.82 21.93 21.93(Type A) (Type A) (Type B) (Type B) (Type A) (Type A) Moulding density[g/cm³] 1.870 1.870 2.020 2.020 1.870 1.870 Wheel Wheel Type * Type VIType IV Type VI Shape T1MSP T1MSP T1MSP Dimension 600 × 65 × 203, 600 ×65 × 203, 600 × 65 × 203, 2 V = 20° U = 1 2 V = 20° U = 1 2 V = 20° U =1 **(see Table 1)

B. Testing Procedure

The grinding wheels prepared as in Example IX were tested in acreep-feed grinding application in order to establish the grindingperformance of the wheels. Using the wheels of Example IX, grindingtests were performed using the following grinding conditions

-   Grinding Process: creep-feed grinding-   Machine: Magerle MGC-   Workpiece: saw blades, to be ground: 2×100×110 mm, tooth depth 3 mm-   Parameters: see Table 17, two wheels in a set for grinding both    sides of workpiece-   Dressing: diamond rotary dressing tool, synchronous dressing, ratio    of surface speeds of grinding wheel and dressing roll 0.75

C. Results

TABLE 17 Results for Example IX Comparative Example Example Ref. IX-3Example IX-1 IX-2- Operating speed v_(c) 45 49 40 [m/s] Feed rate 5501200 800 v_(W)[mm/min] Dressing 2 × 0.03 mm 1 × 0.03 mm 1 × 0.02 mm

The main improvements of the test specifications can be referred to anincrease in the feed rate and to the dressing process. The dressingprocess was improved by reducing the number of dressing cycles by 50%.For Example IX-1 the dressing amount was kept constant but in total wasreduced by 50% (0.03 mm instead of 0.06 mm). For Example IX-2 thedressing amount was decreased to 0.02 mm this in total reflecting animprovement by ca. 65%. Due to the machine settings no further variationof the grinding parameters could not be tested. Even with thisrestriction an increase of the feed rate by 45-120% was obtained.Additionally considering the dressing process the efficiency of theentire grinding process was improved.

1. A bonded abrasive article comprising shaped abrasive particles and abonding medium comprising a vitreous bond, said shaped abrasiveparticles each comprising a first side and a second side separated by athickness t, wherein said first side comprises a first face having aperimeter of a first geometric shape, wherein the thickness t is equalto or smaller than the length of the shortest side-related dimension ofthe particle.
 2. The article according to claim 1, wherein the shapedabrasive particles are ceramic shaped abrasive particles.
 3. The articleaccording to claim 1, wherein the shaped abrasive particles comprisealpha alumina.
 4. The article according to claim 1, wherein the shapedabrasive particles comprise seeded or non-seeded sol-gel derived alphaalumina.
 5. The article according to claim 1, wherein said shapedabrasive particles comprise a major portion of aluminum oxide.
 6. Thearticle according to claim 5, wherein said aluminum oxide is fusedaluminum oxide.
 7. The article according to claim 1, further comprisingsecondary abrasive particles.
 8. The article according to claim 7,wherein the shaped and secondary abrasive particles are independentlyselected from particles of fused aluminum oxide materials, heat treatedaluminum oxide materials, ceramic aluminum oxide materials, sinteredaluminum oxide materials, silicon carbide materials, titanium diboride,boron carbide, tungsten carbide, titanium carbide, diamond, cubic boronnitride, garnet, fused alumina-zirconia, sol-gel derived abrasiveparticles, cerium oxide, zirconium oxide, titanium oxide or acombination thereof.
 9. The article according to claim 7, wherein thesecondary abrasive particles are selected from crushed abrasiveparticles having a specified nominal grade.
 10. The article according toclaim 9, wherein the crushed abrasive particles are of a smaller sizethan the shaped abrasive particles.
 11. The article according to claim 7wherein said secondary abrasive particles are selected from particles offused aluminum oxide materials, particles of superabrasive materials orparticles of silicon carbide materials.
 12. The article according toclaim 1 comprising 10 to 80% by volume of said shaped abrasive particlesand 1 to 60% by volume of said bonding medium.
 13. The article accordingto claim 1, wherein said vitreous bond comprises, based on the totalweight of the vitreous bond, 25 to 90% by weight of SiO₂; 0 to 40% byweight of B₂O₃; 0 to 40% by weight of Al₂O₃; 0 to 5% by weight of Fe₂O₃,0 to 5% by weight of TiO₂, 0 to 20% by weight of CaO; 0 to 20% by weightof MgO; 0 to 20% by weight of K₂O; 0 to 25% by weight of Na₂O; 0 to 20%by weight of Li₂O; 0 to 10% by weight of ZnO; 0 to 10% by weight of BaO;and 0 to 5% by weight of metallic oxides.
 14. The article according toclaim 1, wherein the vitreous bond is obtainable from a vitreous bondprecursor composition comprising frit.
 15. The article according toclaim 1, comprising porosity.
 16. The article according to claim 7wherein the shaped abrasive particles and the secondary abrasiveparticles are comprised in a blend, wherein the content of the secondaryabrasive particles is up to 95% by weight based on the total amount ofabrasive particles present in the blend.
 17. The article according toclaim 1, wherein said first geometric shape is selected from polygonalshapes, lense-shapes, lune-shapes, circular shapes, semicircular shapes,oval shapes, circular sectors, circular segments, drop-shapes andhypocycloids.
 18. The article according to claim 1 wherein said firstgeometric shape is selected from triangular shapes and quadrilateralshapes
 19. The article according to claim 1, comprising at least onesidewall.
 20. The article according to claim 19, wherein the at leastone sidewall is a sloping sidewall.
 21. The article according to claim1, wherein said shaped abrasive particles each comprise at least oneshape feature selected from: an opening, at least one recessed (orconcave) face; at least one face which is shaped outwardly (or convex);at least one side having a plurality of grooves or ridges; at least onefractured surface; a low roundness factor; a perimeter of the first facecomprising one or more corner points having a sharp tip; a second sidecomprising a second face having a perimeter comprising one or morecorner points having a sharp tip; or a combination of one or more ofsaid shape features.
 22. The article according to claim 1, wherein theshaped abrasive particles each have an opening.
 23. The articleaccording to claim 1, wherein the shaped abrasive particles furthercomprise a plurality of grooves and/or ridges on the second side. 24.The article according to claim 1 wherein the second side comprises avertex or a ridge line or a second face.
 25. The article according toclaim 24, wherein the second side comprises a second face separated fromthe first side by thickness t and at least one sidewall connecting thesecond face and the first face.
 26. The article according to claim 25,wherein the second face has a perimeter of a second geometric shapewhich may be the same or different to the first geometric shape.
 27. Thearticle according to claim 26 wherein said first and second geometricshapes are independently selected from regular polygons, irregularpolygons, lenses, lunes, circulars, semicirculars, ovals, circularsectors, circular segments, drop-shapes and hypocycloids.
 28. Thearticle according to claim 26 wherein the first and second geometricshapes have identical geometric shapes which may or may not be differentin size.
 29. The article according to claim 28, wherein said identicalgeometric shapes are both selected either from triangular shapes or fromquadrilateral shapes.
 30. The article according to claim 25, wherein thefirst face and the second face are substantially parallel ornon-parallel to each other.
 31. The article according to claim 25,wherein the first and/or the second face are substantially planar. 32.The article according to claim 25, wherein at least one of the first andsecond face is a non-planar face.
 33. The article according to claim 32,wherein at least one of the first and the second face is shapedinwardly.
 34. The article according to claim 33, wherein the first faceis shaped inwardly and the second face is substantially planar or thefirst face is shaped outwardly and the second face is shaped inwardly orthe first face is shaped inwardly and the second face is shapedinwardly.
 35. The article according to claim 25, wherein the second sidecomprises a second face and four facets intersecting the second face ata draft angle alpha forming a truncated pyramid.
 36. The articleaccording to claim 24, wherein the second side comprises a vertexseparated from the first side by thickness t and at least one sidewallconnecting the vertex and the perimeter of the first face.
 37. Thearticle according to claim 36, wherein the perimeter of the first faceis trilateral, quadrilateral or higher polygonal and wherein the secondside comprises a vertex and the corresponding number of facets forforming a pyramid.
 38. The article according to claim 37, wherein theperimeter of the first face is trilateral and wherein the shapedabrasive particles have four major sides joined by six common edges,wherein each one of the four major sides contacts three other of thefour major sides, and wherein the six common edges have substantiallythe same length.
 39. The article according to claim 24, wherein thesecond side comprises a ridge line separated from the first side bythickness t and at least one sidewall connecting the ridge line and theperimeter of the first face.
 40. The article according to claim 39,wherein the sidewall comprises one or more facets connecting the ridgeline and the perimeter of the first face.
 41. The article according toclaim 39, wherein the first geometric shape is selected fromquadrilateral geometric shapes and the sidewall comprises four facetsforming a roof-shaped particle.
 42. The article according to claim 1having a three-dimensional shape selected from the shape of a wheel,honing stone, grinding segment, mounted points, or other shapes.
 43. Thearticle according to claim 1, wherein the article comprises a wheel. 44.The article according to claim 43, wherein the wheel is selected fromgrinding wheels for cylindrical grinding, centerless grinding, surfaceand profile grinding, reciprocating grinding, creep-feed grinding,grinding in generating methods of gears, threads, tools, camshafts,crankshafts bearings, and guard rails.
 45. The article according toclaim 1, wherein the shaped abrasive particles are homogeneouslydistributed in the abrasive article.
 46. The article according to claim1, wherein the shaped abrasive particles are non-homogeneouslydistributed in the abrasive article.
 47. The article according to claim46, which is or comprises a bonded abrasive wheel, the wheel comprisingan outer zone and an inner zone, wherein the compositions of the innerand outer zone differ in one or more aspects selected from thecomposition of the bond, the shape of abrasive particles, the grit sizeof abrasive particle, and the amount of abrasive particles.
 48. A bondedabrasive article according to claim 1, wherein the article comprises ablend of said shaped abrasive particles and secondary abrasiveparticles, wherein the amount of shaped abrasive particles ranges from20 to 60% by weight, based on the total weight of abrasive particles inthe blend.
 49. A bonded article according to claim 1, wherein thearticle is an article for gear grinding.
 50. Use of an article accordingto claim 1 in high performance grinding applications.
 51. Use accordingto claim 50 for outer diameter grinding with a Q′_(w) of at least 1.5mm³/mm/sec, inner diameter grinding with a Q′_(w) of at least 1mm³/mm/sec, surface grinding with a Q′_(w) of at least 1.5 mm³/mm/sec,profile grinding with a Q′_(w) of at least 3 mm³/mm/sec, profilegrinding with generating method with a Q′_(w) of at least 8 mm³/mm/sec,creep-feed grinding with a Q′_(w) of at least 4 mm³/mm/sec, and camshaftgrinding with a Q′_(w) of at least 8 mm³/mm/sec.
 52. Use of an articleaccording to claim 1 for abrading a workpiece material selected fromsteels, non-ferrous metals, alloys, hard metals, ceramics and glasses.53. Method for abrading a workpiece, the method comprising frictionallycontacting at least a portion of the abrasive article according to claim1 with a surface of a workpiece; and moving at least one of theworkpiece or the abrasive article to abrade at least a portion of thesurface of the workpiece.
 54. Method of gear grinding characterized byusing a bonded abrasive article according to claim
 1. 55. Method ofcreep-feed grinding characterized by using a bonded abrasive articleaccording to claim
 1. 56. Method of surface grinding characterized byusing a bonded abrasive article according to claim
 1. 57. Method ofcylindrical grinding characterized by using a bonded abrasive articleaccording to claim
 1. 58. A method of grinding characterized by using abonded abrasive article according to claim 1, wherein the specific chipvolume V′_(w) is at least 20% higher, than the specific chip volumeachieved when using a comparable bonded abrasive article at the samespecific material removal rate Q′_(w).